Rally Computer



This manual explains the installation and operation of the Zeron 660 rally computer. Operating procedures for many different rally situations have been included, but obviously it is not possible to cover all of those you may encounter. A thorough knowledge of how your computer works will help you adapt these instructions to local customs.

It is highly recommended that you read this manual carefully and then practice before you compete on an event. An old rally, rerun without the pressure of staying on time, can check your mastery of the instrument.



Your computer utilizes one of the newer integrated circuit technologies which is susceptible to damage by static electricity, e.g., the kind that shocks you after walking across a rug on a day when the humidity is low. Therefore, several precautionary steps should be followed when you handle the 660. There is no danger of harming any of the electrical components when the unit is in its case. If you must remove it from the case, handle it by the front panel. Try to discharge yourself before you start by touching a metal object. Once it is out, avoid contact with the printed circuit boards and the components mounted on them. Don't worry if you accidentally touch one of the prohibited areas. Most likely no harm was done.

Mounting studs are located on the top and back of the case. Refer to the illustrations at the end of the manual should you find it absolutely necessary to drill more holes. If you intend to use the 660 on performance type events, support the case along the bottom so that all shock and jolt forces are not taken by the mounting studs (the case my crack). The 660 will slide out of its case after you remove the screws in the four corners of the front panel. The connecting cables and the readout will slip out through the cutout in the back of the case.

The heat sink that protrudes from the back of the case is connected to the +12 volts side of the car's electrical system. Be positive that it cannot touch the car's chassis or other metal parts mounted to the chassis. This won't hurt the 660 but it will blow the fuse and shut you down. The heat sink, as you might imagine, gets hot. It will not hurt your car but it will surprise you if you reach around behind the case and touch it.

The 660 is built around components that operate at temperatures between -40 and +85 degrees centigrade. Operation outside this range will not harm the unit but may cause it to calculate incorrectly. While you won't be rallying at the low end, temperatures at the high end are possible under certain conditions. On hot days when the car is closed and in direct sunlight, temperatures on the dash may exceed the upper limit. Watch out for this at rest stops and lunch breaks. Park in the shade or so the dash is not in sunlight. It's also advisable to turn the displays off. This has several advantages. First, there is little danger of the computer over heating because it's in a poor location. Second, the computer draws only 0.06 amp (instead of 1.5 amp) so it can't run down a weak battery. Finally, your competition won't be able to check their mileage and computed time by comparing with you.


The driver readout is connected to the computer by a 4 foot cable. Mount the readout in front of the driver so it can be easily read at a glance. The proper locations for mounting screws or straps will be apparent once the cover is removed. Apply the same precautions for the electronics and temperatures that we mentioned above.

Sending Units:

Disconnect the odometer cable from behind the speedometer, insert the sending unit, then reconnect the cable at the end of the sending unit. Make sure that the square pin is in place to drive the speedometer. The cable should turn evenly without binding. A small amount of speedometer needle bounce at low speeds is normal; large fluctuations indicate a binding cable. Check for sharp bends that way have been placed in the cable when you instilled the sending unit. It might be helpful to change the position of the cable or to rotate the sending unit on the back of the speedometer.

The sending unit can also be driven from a dead-wheel cable or from an auxiliary cable connected thru a 1:1 tee to the odometer cable. In either of these two cases, static electricity might develop in the cable and cause false inputs to the 660. Ground the sending unit by running a wire between it and the car's chassis. This will keep any electrical noise out of your computer.

The sending unit is not weather proof so it may be damaged if left exposed. Always mount it inside the passenger compartment. When your sending unit is not mounted beneath the dash, try to keep it out of direct sunlight. High intensity light may leak in thru the mating surfaces and cause the unit to operate improperly.

Standard Halda T fittings are used at each end. If you change cars, these can be replaced with a different type. It may then be necessary to adjust the washers located on the rotor. The bent washers apply a slight drag to the rotor as it turns. This prevents extraneous vibrations from causing false outputs. Increase or decrease the drag by bending a washer(s) until the rotor offers a small resistance when turned. Check the drag every 10,000 miles when the unit is permanently installed in your car.

Most cars use odometer cables which terminate with a 0.106 inch square shaft. Many British and French cars use a 0.118 inch shaft. Your sending unit comes equipped with the proper rotor for your car. Should you switch cars and need the other size, it can be ordered from the price list found at the end of the manual.

Electrical Connections:

A pre-wired power connector is included with the 660. Connect the red wire to +12 volts (uninterrupted by the ignition switch), the black wire to ground. Attach the leads as securely as you can make them. A power loss, either +12 volts or ground, will erase all of the data in the displays. For this reason you should not select a power lead from under the dash. It may contain numerous slip-on connectors as it is routed from point to point. Your best tap point is to the fuse box where the main power lead enters. If there are no screw on terminals in the fuse box, strip back the insulation on the power lead and attach the red wire there. Solder and then wrap with electrical tape for a secure joint. Attach the ground lead beneath a screw mounted in a metal part which leads to the car's main chassis. Scrap away any paint that might cause a poor electrical path. Using a cigarette lighter is inviting disaster.

Notice that the power connector has 4 pins instead of only 2. The pins are wired in pairs, two for +12 volts and two for ground. If your installation requires additional connectors, follow this procedure of doubling up on the pins. This is another precaution against a momentary power interruption.

A 3 or 4 amp fuse is located in the +12 volt wire on the power connector. Never run your 660 without the fuse in place. It is your protection against shorting the heat sink or mistakenly reversing the power leads. A replacement is taped to the back of the case. In the unlikely event additional fuses are needed, they can be found at most service stations and TV repair shops. In desperate circumstances a fuse of higher rating is OK, just remember to put the correct one in later.

Accidentally reversing the power leads will not harm your 660. It won't turn on. The fuse will blow if the sending unit was connected when the leads were reversed.

Keep the pins on the sending unit and power connectors free from dirt and grime. A light brushing once a year will steel wool will keep the pins in good condition. Never wrap masking tape around the pins. The gum from the tape attracts dirt. You can use tape to hold the connectors together if you think they might separate because of the way they are located in your car.

Two final items concerning your 660 and the car's electrical system need mentioning. First, the 660 will operate on voltages from 7 to 17. Go below 7 volts and information will start dropping out of the displays. Your car's output voltage normally varies between 10 volts when starting and 15 volts when charging. A good battery is your beat protection against the voltage falling below 7 volts.

Second, while the car's nominal output voltage is 12-14 volts, electrical noise and large voltage spikes are often present at the same time. Your computer has adequate protection to isolate it from most noise sources (lights, fans, etc.). The one exception is solid copper ignition wires. Few cars come equipped with these wires as standard equipment (Alfa Romeo's do). They need to be replaced with regular carbon resistance wire if your car has them. Don't forget the wire between the coil and the distributor.

You may be tempted to "see what happens" before changing the wires. In some cases the effect is obvious. The counters begin rapid and sporadic counting as soon as the car is started. Other times, hours of close observation may indicate that all is well. Do not be misled by this apparent lack of trouble. This type of noise is very elusive. Why risk getting bad checkpoint scores? Change the wires!

Porsche owners relax. The models with solid wires are also equipped with suppressers that eliminate the noise radiated by the wires.

A small gooseneck lamp to light the 660 during night rallies is available thru the price list at the end of the manual. Two tapped holes are located on the front panel for mounting and a power jack is provided on the back of the case. The lamp comes with a pre wired plug, spare bulb, and on/off switch. If you want to run your own lighting system, do not use the jack and do not use the front panel as a ground connection. Doing so may overload the 660's electronics and cause a failure.


As you can see from an examination of the front panel, the 660 does not have many of the control switches found on other rally computers. At first glance this may appear to limit the versatility of your computer. However, as you continue with the manual you will discover how many of the operating functions have been combined to make the 660 nearly error proof yet still allow it to handle almost every rally situation. A sample rally is given to illustrate what actions you would take during an actual event.


When the 660 is first turned on, the displays will show a meaningless pattern of digits and, in some cases, blank digits. This random pattern will also warn you that the computer has lost power. If it occurs during your shakedown drives, a faulty power connection must be found and eliminated.

The Odometer records official rally miles from 00.00 to 99.99 in increments of 0.01 mile. Once the computer is corrected at the end of the odo leg, the Odometer will match the rally's mileage. The count direction, up or down, is controlled by switches you will read about later. To zero the Odometer, press the small button to the left of the display while also pressing the button on the lower right side of the front panel. The second button, referred to as the "safety" from now on, has several purposes. One of them is to prevent you from mistakenly zeroing the Odometer. Because it must be pressed along with the other button, an unintentional bump on the zeroing button won't cause the loss of your mileage.

The Auxiliary counter has three modes. The toggle switch at the left of the display selects the one that's needed. Mileage in hundredths of a mile is recorded when the switch is in the DIST (distance) position. Use it for actions keyed to short distances. For example, "Left 2.67 miles after county line". The TIME mode is used for similar instructions. The "time" recorded is computed time, not real time. When the car is not moving, time does not register.

When switched to P/G, the Auxiliary registers the amount of any pauses or gains entered into the computer. The pause or gain procedure will be discussed later. For now, it's only important to learn that they register here in the middle counter. The toggle switch normally remains in the P/G position. After a pause or gain is registered, zero the counter so it's ready for the next action. You don't need the safety to zero. Because the Auxiliary spends most of its time at 000, there is little chance of losing its data accidentally.

In place of a fourth digit, the Auxiliary has a warning flasher to alert you, whenever a rotary switch is not in a normal operating position --- ON COURSE and PAUSE.

The counter, therefore, only counts to 9.99 where it starts over at 0.00. Most time and distance related actions are keyed to short increments. Time or distance can be added directly to the readings in the CTC or Odometer for long increments.

The Clock shows real time of day from 00.00 to 59.99 minutes. It restarts each hour at 00.00. Zero the Clock with the push button and the safety.

The time calculated by the 660 is recorded in the Computed Time counter (CTC). It counts in decimal minutes from 00.00 to 59.99. Its count direction is also controlled by switches you will read about later. Again, the safety must be pressed to zero.

The display's intensity is determined by the switch located to the right of the Odometer. Use the BRT (bright) position for daytime rallies, the DIM for night ones. The OFF position turns the displays completely off.

Correction Factor:

The computer correction factor adjusts the sending unit pulses to allow the 660 to run at official rally miles. The four digit factor is set in the switches marked FACTOR.

The formula for adjusting your factor at the end of the odo leg is:

                                   OFFICIAL MILES
                      NEW FACTOR = -------------- X OLD FACTOR
                                   COMPUTER MILES

Examples: Your factor at the start of the odo leg is 4800. The odo leg is 14.92 miles long and the Odometer reads 15.07.

                                ----- X 4800 = 4752

4752 is your factor for the remainder of the event. Of course, you can change it should conditions later require you to.

Before you run your first rally you may want to obtain a base correction factor (BCF). This is the factor which runs the 660 at statute miles in your car. Once obtained, make a habit of starting every rally with this factor. Your BCF will normally keep you within a few percent of rally mileage so the odo leg will be easier to run.

To establish a BCF, it will be necessary to run the car against a known statute distance. Many highways have mileage markers or you can use an old rally measured in statute miles. When a suitable course is not available, lay one out using the car's odometer. A more precise BCF can be developed when the opportunity arises.

The course you select can have any length although it's a good idea to make it at least 5 miles. Set a factor of 5000 and run the course. Use the formula to calculate your BCF. A rerun of the course with the new factor will find your Odometer mileage equal to the course's "official" length.

Your exact statute mile factor does not need to be your BCF. Your calculation will be easier if you round off the last two digits. 5529 would go to 5500, 3579 to 3600, and 4841 would round to 4800.

There may be times (it may start raining) when you will want to adjust your factor during the rally. Small changes can be mentally calculated quite easily. For each 0.01 mile you wish to adjust your mileage in 10 miles, change the factor by the value of its first digit. Increase the factor to increase your mileage. For less mileage, decrease the factor.

Suppose your factor was 6012 and you wanted to increase your mileage 0.01 mile for every 10 you travel. Change the factor to 6018 (6012 + 6). As another example, your factor is 4850 and you need a decrease of 0.02 mile per 10 miles. Change the factor to 4840 (4850 - 4.8 - 4.8).

If you know the number of revolutions per mile at the input of the sending unit, you can calculate your BCF from the formula below. A little math will tell you that you need a minimum of 480 revolutions per mile to run the computer. Most cars have between 800 and 1600. None are lower. Direct drives from an undriven wheel vary between 800 and 1000 depending on wheel size.

                             CORRECTION FACTOR = --------------------
                                                 REVOLUTIONS PER MILE

Most American cars and many foreign models have 1000 revolutions per mile at their odometer cables. The BCF in these cases would all be around 4800.

The 660 will also run in kilometers. The correction factor has been designed so that it will not normally go above 6000. This gives you sufficient range to increase the factor to let the Odometer read 1.00 at the end of 0.62 mile (1 kilometer = 0.62 mile .... old factor x 1.61). The 660 doesn't know or care what the unit of measurement is. That's for you to decide. Of course, speeds are now entered in KPH, not MPH.

Speed Banks:

Rally speeds are set in miles per hour with the switches located at the top of the computer. The correction factor corrects the entire computer, therefore the speeds you enter are the ones given in the route instructions. There's no need for corrected tables, conversion factors, etc. Any speed from 00.3 to 99.9 mph in increments of 0.1 mph can be used. Speeds of 00.0, 00.1, and 00.2 all compute as zero miles per hour, i.e., no computed time is generated as the car moves.

The toggle switch between the two banks selects the active bank. The unused bank can be preset to the next rally speed. You may change the active bank's speed while the car is moving. This technique is helpful with small repetitive changes, say from 40 to 41 to 42. Don't use this with large changes. If you were not observant, you might momentarily have a very low speed in the bank as you change from one speed to another. Only 10 feet at 1 mph is enough to get you a 5 or 6 penalty at the next checkpoint. The best rule is entering the unexpected or forgotten speed in the unused bank and then throwing the switch.

Avoid extremely slow speeds whenever possible. This is one time when the 660's accuracy may hurt your score. Consider the following instructions taken from an actual rally.

            34.45  33.  "Stop".  Change average speed to 1 mph.
            34.92  34.  "Go".  Change average speed to 35 mph.

The time for this distance is 28.20 minutes. The rallymaster was giving the crews a break at the gas station which occurred between the two instructions. When he measured the course, he rounded off the mileages to the nearest hundredth. Since he gave you two hard mileages, the time of 28.20 was correct. However, the 660 calculates on pulses received every 3-4 feet. If the actual distance were 0.474 miles, the 660 would have calculated a time of 28.44 minutes -- a 0.24 minute error at the next checkpoint! You should treat this type of problem as a transit zone of 28.20 minutes. No reasonable rallymaster would expect you to maintain speeds this low. He would expect you to be able to calculate the elapsed time given the speed and distance.

Checkpoint Switch:

This control locks the data displayed in the Odometer, Clock, and CTC whenever it is thrown to "checkpoint". The counters continue to function, but their additional data is not shown until you return the switch to the off position.

Throw the switch as you cross checkpoint timing lines. The mileage to the line, your actual arrival time, and your computed arrival time will then lock in the displays. If you are mistimed, the Clock will verify the time you want. After you have recorded whatever information you desire, throw the switch off.


The readout displays the computed time error. This is the difference between the Clock and the CTC. As will be illustrated later, you will rally on a time-of-day basis. That is, when you are "on time", the time in the Clock will be the same as the time in the CTC. When the times diverge, the readout shows the error.

Examples are:       012 --  0.12 minute ahead ("up")
                    001 --  0.01 minute ahead
                    000 --  on time
                    998 --  0.02 minute late ("down")
                    972 --  0.28 minute late

As you can see, the readout drops below 000 when you are late. It may occur to you that a + or - indicator would make the driver's job easier. However, as you gain experience, you will find that driving a little up is the most effective tactic for getting good scores. Since you will then spend most of your time up a hundredth or two, a reading such as 002 will automatically indicate that you are ahead. It won't be necessary to associate an extra piece of data (the + or -) with the numbers each time the readout is checked.

Mental arithmetic when you are extremely late is not required in most cases. Suppose you found yourself delayed by traffic and when you checked the readout it read 861. In this type of situation, it's more important to get back on time, not worry about being precisely 1.39 minutes late.

The relationship among the Clock, CTC, and readout are illustrated below:

                      CLOCK       CTC         READOUT
                      0000        0000        000 (on time)
                      0122        0000        878 (1.22 late)
                      0122        0200        078 (0.78 early)
                      1234        1240        006 (0.06 early)
                      1234        2240        006 (10.06 early)

Notice how the readout in the last example appears to indicate that you are only up 0.06 minutes when you are really up 10.06 minutes. You must always insure that the Clock and CTC are in the same 10 minute period. Though there is little chance for this to happen while you rally on time, you should compare the counters at the end of the odo leg, the end of transit zones, and whenever you recover from being off course.

You will soon notice that the readout does not display all the Clock and CM pulses. If the car is stopped, the readout counts steadily downward as the Clock counts up. Once you are up to rally speed the readout will hold a constant value even though the Clock and CTC are trying to pulse it up 1 count, then down 1 count, then up 1. The driver can hold the readout at a constant number without the distraction of digits flipping up and down. This fixed number system is achieved by updating the readout once every 0.01 minute. Because of this, you may see the readout skip some numbers as you watch it count. This is normal. It only means that the readout received several pulses during the 0.01 update interval.

The driver can also use the readout for pauses and gains. Suppose the Route Instructions called for a pause while the navigator was busy. You can run the pause on the readout until the navigator is free to enter it normally. If the pause were 0.25 minutes, slow the car until the readout drops to 975 (0.25 minute late). Then continue with 975 as your 'on-time' reference instead of 000.

Mileage Alarm:

A preset mileage can be dialed into the 3 switches below the CTC. When the Odometer reaches this mileage, a buzzer will sound to alert you to this fact. The system is turned on and off by the switch to its left. Any mileage from 00.0 to 99.9 in steps of 0.1 mile can be set. The alarm will sound for a minimum of 0.1 mile after the selected distance is reached. In most cases however, you will switch the buzzer off once it starts. The alarm may also go off at random mileages if it is left on past the preset amount. Keep the system off until you set in a new unreached mileage.

You do not want the buzzer to go off exactly at the mileage you are concerned with. Setting to a mileage slightly prior to the desired one will give you time to prepare for the action. Therefore, you only need mileage settings to the nearest 0.1 mile.

Mode Control:

This rotary switch selects the operating mode for all of the 660's functions. The 660 is off when the switch is in the OFF position. All others are operating ones.

DIST (distance only) and DIST REV (distance only reverse) - These modes are used when computed time is not required, e.g., during an odo leg or transit zone. The Odometer and Auxiliary will both register distance. No computed time is registered in the CTC. As will be explained shortly, you are not prevented from adjusting the CTC with the add time push buttons. This allows you to set the CTC to your time out from the end of the odo leg as you run the leg. You can also add in a transit zone time as you complete the distance.

ON COURSE - This is the normal operating mode for the 660. Both the Odometer and CTC count forward. The warning flasher indicates when the switch is not in this position.

OFF COURSE - Both Odometer and CTC are reversed. Since the readout follows the CTC, it also is reversed. Use this mode to retrace the rally course after a course following error or to back up to check a clue.

PARK - This position turns off the 660's calculating functions. No mileage or computed time are allowed into the counters although the add pulse circuits still operate. Use it whenever you wish to leave the rally course during a break. The blank positions on the switch are also PARK. If you accidentally overshoot one of the operating positions you won't turn the 660 off or put it in TEST.

The PARK mode also comes in handy when you are off course. Once you've decided to turn around, pick out a landmark (tree, pole, etc.) and switch to PARK as you pass It. U-turn at the first opportunity and switch to OFF COURSE as you pass the landmark from the other direction. This procedure eliminates guessing at when to reverse the 660 as you turn around. Switch directly to ON COURSE when you regain the rally route.

TEST - This mode activates an internal pulse generator to run the 660 as if it were in a moving car. You can test or demonstrate the computer with this mode. Using a correction factor of 5860, the 660 behaves as if were in a car going 60 mph.

Pulse Control:

You will use this switch, in conjunction with the push buttons, to pause or gain, add or subtract computed time, add or subtract mileage, and set the Clock. The rotary switch selects the destination of the pulses, the push buttons the amount. For example:

Pause 2 minutes 30 seconds -- Set the selector to PAUSE, press the 1.00 (100 pulses) button 2 times and the .10 (10 pulses) button 5 times. Remember, you must convert the seconds to hundredths.

For pauses and gains, the pulses go into the CTC and also register in the Auxiliary if it's in the P/G mode. The Auxiliary will double check your pushes. If the Auxiliary were in use with a distance turn, the pause would still go in but you could not check yourself.

Since pauses and gains are simply the addition and subtraction of computed time, you can use these two positions whenever you need to set the CTC to a specific time. To illustrate, you will set the CTC to your time out from the end of the odo leg. The CTC won't be counting as you run the leg so simply use the push buttons to set in the time you want. Suppose this time was 48.00 minutes. Assuming the CTC was at 00.00, turn the switch to GAIN and push the 1.00 button 12 times to subtract 12 minutes. At checkpoints you will use the same method to set the CTC to your assigned time out. The same is true for transit zones and time of day restarts.

+ DIST and - DIST adjust your Odometer. They are needed at the end of the odo leg to set your Odometer to official mileage, to adjust for wheel slippage, and to correct the Odometer at checkpoints where your mileage is in error.

Of course, all of the above procedures apply whether or not the car is moving. It makes no difference to the computer.

The Auxiliary counter does not register added or subtracted pulses in the time or distance modes. For example, a pause entered while the Auxiliary was in use with a timed turn would go into the CTC but not into the Auxiliary. To complete the timed turn, just reduce the amount of time you are seeking in the Auxiliary by the amount of the pause. When you anticipate pauses or gains during a time based action, it's easier to use the CTC as your reference. Suppose the CTC reads 34.91 minutes as you pass a clue that requires a turn 4.78 minutes later. Simple addition indicates that the turn will occur when the CTC reads 39.69. The rallymaster took into account any pauses and gains which occurred in the 4.78 minutes. Enter them as usual and turn when the CTC reads 39.69.

Keep the rotary switch in the PAUSE position except when you are using it specifically for other actions. Pauses occur most often between checkpoints. The flasher will remind you when the switch is in another position. Hopefully this will prevent your next pause from going into the Odometer.

One last item will complete this section. Pulses add or subtract as directed by the rotary switch. The Mode Control switch does not affect their direction. Even when this switch is in OFF COURSE, pulses add or subtract as usual. If you go off course and enter a pause before you recognize your error, you would enter a gain on the way back. A gain would be a pause as you return to the rally route.

Setting the Clock:

To set the Clock you will use the PAUSE position on the Pulse Control, the push buttons and the safety. When the safety is depressed, the 1.00 and .10 buttons add time to the Clock. The .01 button will stop the Clock. The Clock runs at all times except when these two buttons are used together. The following example illustrates the simplest method for setting the Clock to time of day. It will be assumed that you are using the short wave radio signals of either WWV or CHU for your time reference.

Just prior to an even minute, push the safety and .01 button to stop the Clock. Next, depress the zero button next to the display. Since you have the safety in, the Clock will go to 00.00 and hold there. When the even minute tone sounds, release the buttons. The first Clock count will occur exactly 0.01 minute later. The hundredths part of the Clock counter is now set. Next, push in the safety again and, using the 1.00 button, run the minutes up to the correct value. The whole procedure will normally take about 20 seconds after a little practice.

There are other ways by which to set the Clock. You can run the Clock up to slightly ahead of real time, hold it there, then start it when that time arrives. However the method described first is usually the easiest and fastest. Remember that if you push any of the buttons without the safety, time will go into the CTC. As you set the Clock, the pushes will also register in the Auxiliary counter if it's in the P/G mode. Simply zero the counter when you are finished.


Install the computer and check that it's properly connected and in good working order before you leave home. As with all rally equipment, the 660 is useless when part of it is home in the closet while you are at the start.

Let's assume:  1.  The first car leaves at 8:01.00 AM.
               2.  Your car number is 10
               3.  Your BCF is 4800
               4.  The general instruction require a speed change to 35 mph whenever
your                                                                                                mileage
is an even multiple of 22.00 miles (22, 44, 66, etc.)

Turn the computer on about 30 minutes before your time to leave the start. Zero the counters and set the Clock. Enter your BCF. Dial 21.9 miles into the mileage alarm system and switch it on. The remaining time can be spent double checking things in the car and going over the generals one final time.

      0.00  1.  Begin odometer correction leg.  Leave this point at 8 AM plus your
                car number in minutes.  Take 30 minutes to reach instruction 8.

Check your Odometer to see that it's zeroed, be sure you are in DIST, get your route instructions, then leave. As you run the odo leg, set the CTC to your time out from the end of the odo leg (40.00). Enter the first two rally speeds.

      8.93  8.  End odometer correction leg at "Stop".  Begin 35 mph.

Write down the mileage in the Odometer (let's call it 8.82), adjust it to 8.93, switch to ON COURSE, then pull ahead to clear the area for other cars. The CTC will begin to count up based on the first rally speed. The new correction factor is not in yet, but a short distance at the old one will not give you a timing error.

Calculate and enter the new factor. (4860)

As Clock time begins to catch up with the time in the CTC, your readout indicates the time that remains before you are due to leave. Get the car up to rally speed as the readout nears 000. Be sure that the Clock and CTC are in the same 10 minutes.

CHECKPOINT! Throw the Checkpoint switch as you cross the timing line. Compare the Clock time with that given you by the checkpoint workers. If there's a discrepancy, straighten it out before you release the switch. Turn the switch off and pull up to the outmarker. Adjust your Odometer if necessary.

Most rallys use one of two common methods to start you on the next leg. When the Checkpoint zone is dead mileage, i.e., timing is from outmarker to checkpoint line, the 660's procedure is effortless. At the outmarker, pulse the CTC up to your assigned time out. Assuming that you have been given adequate time by the workers, the CTC will then have more time in it than the Clock has. The readout will indicate the time left before you start the next leg. Pull ahead slightly to clear the outmarker for other rally cars. Begin the next leg as the readout nears 000.

When a rally is timed from checkpoint line to checkpoint line (no dead mileage), the calculated time between the checkpoint line and the outmarker must be added to your time out. For example, you are given a time out of 9:53.00 and you are now at the outmarker 0.10 mile away. Pulse the CTC to 53.00 plus the calculated time from the checkpoint line. In this case if your speed was 40 mph, the CTC would be set to 53.15. Again, you would pull ahead to wait out your extra time.

You can obtain the checkpoint zone time by several methods. First, you can note the difference in the CTC readings for the timing line and the outmarker. Second, you can switch the Auxiliary to Time as you cross the line. It's reading at the outmarker will be the computed time for the zone.

Lastly, you can arithmetically calculate the time. Considering the habits of good rallymasters, this last method is probably the most accurate. Also, if the rally speed is changed on the checkpoint slip, the time the 660 is calculating cannot be used. The manual's section on rally math provides an easy method for calculating this time yourself.

      21.9 miles --- the buzzer will sound.  Enter 35 mph in the inactive bank in
                     preparation for the speed change at 22.00 miles.  Dial in 43.9
                     (or the next important mileage).

      28.36  23.  Begin transit zone of 20 minutes to the next instruction.
      28.90  24.  "Max".  End transit zone and zero your Odometer.  Begin 40 mph.

At 28.36 miles, switch to DIST and note the time in the CTC. During the transit zone add 20 minutes to the CTC. Plan to arrive at instruction 24 before your time is up. At "Max", set in the new rally speed, zero the Odometer, switch to ON COURSE and pull ahead to wait out the balance of your time. Be sure that the CTC and Clock are in the same 10 minutes when you leave.


Some of the more frequently asked questions about the 660 are:

Q. How accurate is the 660?
A. Your computer is a digital instrument that will compute a perfect time based on the speed and distance inputs. Checkpoint errors result from factors over which you have little control. All things considered, you can expect to average about 0.01 minute error per checkpoint.

Q. How accurate is the Clock?
A. The Clock will stay within 0.01 minute during an all day rally. You can easily adjust it if necessary.

Q. Will shock or vibration harm the 660?
A. While obviously it's not made to be dropped or manhandled, the 660 can withstand all the normal rally jolts and bounces. If you decide to run performance events with your computer, contact Zeronics for the best way to mount the unit in your car.

Q. Can I outrun the 660 by driving too fast?
A. No. You could drive 100 mph with the computer set to 1 mph.

Q. Has anyone ever lost electrical power during a rally?
A. Not when they followed the installation instructions faithfully.

Q. What do I do if the computer breaks down?
A. Your 660 is built with quality parts. However, there is always the chance that it may stop operating correctly. As a first step, you should contact Zeronics and describe the problem in detail. It may not be necessary to return the unit. Most important parts are mounted in sockets for easy removal and replacement.


The math problems you find most often on rallies involve the elements of time, speed, and distance. It is usually easier to work in minutes per mile factors (MPM) than with miles per hour. A factor table has been printed at the end of the manual for your convenience.

For those who are not familiar with MPM factors, a quick explanation is in order. Basically, MPM factors tell how long (in minutes) it takes to run 1 mile at the assigned speed. The factor for 35 mph is 1.714. This means that it takes 1.714 minutes to run 1 mile at 35 mph. Moving the decimal point gives the time for 10 miles (17.14 minutes), 0.10 mile (0.17 minute), and 0.01 mile (0.017 minute--about 2 hundredths).

Notice how MPM factors would quickly solve the checkpoint problem described in the sample rally. In that case, you needed the time for 0.10 mile at 40 mph. A check of the factor for 40 mph (1.1500) tells you it takes 0.15 minute for that distance.

Missed speed changes can easily be "fudged" by using factors. To illustrate, suppose you forgot the speed change that was part of the last route instruction. You've been driving at 30 mph (2.000) instead of 35 mph (1.714). Unless you can risk returning to the execution point, you'll have to make an educated guess at the gain time required to correct the CTC. With the MPM factors, you can quickly see that it takes about 0.29 minute less to run 1 mile at 35 mph than it does at 30 mph. For every mile you've been at the wrong speed, you will have to gain 0.29 minute. Let's say you estimate the distance back to the speed change as 1.5 miles. The amount of the gain would then be 0.44 minute (1.5 X 0.29).

Two helpful formulas are:

                                       60                             Elapsed minutes
            Speed (miles per hour) = ------              MPM FACTOR = ----------------
                                     FACTOR                           Elapsed Miles


Imagine that you are at a checkpoint outmarker and are preparing for the next leg. You set the CTC, check the mileage, then begin to pull ahead to clear the outmarker for other cars. As you do this, you notice that the CTC and Odometer count almost immediately. When you were at the outmarker, you had no way of knowing whether your Odometer pulsed a few feet before you arrived there, or whether it pulsed 50 feet prior to the marker. The same is true of the CTC. Of course it doesn't make any difference where they pulse before the marker, but it would be beneficial if the first mileage pulse occurs 52 feet into the next leg and the first time pulse occurs at the correct mileage for the speed in the computer. The 660 lets you insure that the pulses occur at the proper place. Push the safety before you leave the outmarker. The computer does the rest.

You will want to use this feature at the beginning of the odo leg, at the end of the odo leg, at the end of a transit zone, and whenever the rally's mileage is zeroed. Naturally, when you zero the odometer you also push in the safety. You automatically make the next mileage pulse occur 52 feet later and the next time pulse occur at its proper mileage.

As stated earlier in the manual, when pauses and gains are given in seconds, they must be converted to hundredths. Some values do not convert into even hundredths. Take for example, 10 seconds. In hundredths, this is 16.7. A pause of 10 seconds would be entered as 17. If you had a series of 10 second pauses, putting them all in as 17 would give you an error of one hundredth per three pauses. You can eliminate the problem by making the first two 17 and the third 16.

While all rally teams have a favorite technique for crossing a checkpoint line on time, you may find the following method best suited for the 660.

As you will soon notice, when you are at rally speed and are on time, it's a simple matter to hold the readout at 000. The readout will occasionally count down to 999 or up to 001. You can easily correct this by speeding up or slowing down. But what if the readout changes just before you cross the timing line? You won't have time to correct for it. Even when you can see the checkpoint in the distance, it's impossible to drive the exact rally speed. The readout may still change right at the line.

As an alternative to driving at 000, try driving at 002. Now, when you see the checkpoint, slow down to below rally speed. The readout can only count down. With a little practice, you can make the readout drop to 000 just before the timing line. When a checkpoint occurs without warning, a tap on the brakes will lose the extra time.


Zeronics warrants this product to be free from defects in workmanship and material for a period of one year from original purchase. Our obligation under this warranty is limited solely to repairing or replacing, at our option, any part when the product is returned to us within the warranty period providing: (1) the defective unit in returned to us transportation prepaid by purchaser, (2) no modification or change has been made to the unit's circuitry or wiring, (3) the unit has not been damaged by misuse, neglect, improper operation, accident, or alteration as determined by Zeronics. No other obligation is implied or expressed.


(Subject to change without notice)

The following items are available should you change rally cars or set up a second car.

For a fee of $6.00, you may return your sending unit and have the fittings exchanged for a different type. The present fittings will be kept by Zeronics while the specified ones will be mounted on your sending unit. The rotor drag will be adjusted and the unit will be inspected.


SPEED        SPEED        SPEED        SPEED
   1  60.00    16  3.750    31  1.935    46  1.304
   2  30.00    17  3.529    32  1.875    47  1.277
   3  20.00    18  3.333    33  1.818    48  1.250
   4  15.00    19  3.158    34  1.765    49  1.224
   5  12.00    20  3.000    35  1.714    50  1.200
   6  10.00    21  2.857    36  1.667    51  1.176
   7  8.571    22  2.727    37  1.622    52  1.154
   8  7.500    23  2.609    38  1.579    53  1.132
   9  6.667    24  2.500    39  1.538    54  1.111
  10  6.000    25  2.400    40  1.500    55  1.091
  11  5.455    26  2.308    41  1.463    56  1.071
  12  5.000    27  2.222    42  1.429    57  1.053
  13  4.615    28  2.143    43  1.395    58  1.034
  14  4.286    29  2.069    44  1.364    59  1.017
  15  4.000    30  2.000    45  1.333    60  1.000

                                    OFFICIAL MILES
                       NEW FACTOR = -------------- X OLD FACTOR
                                    COMPUTER MILES

                             60                          ELAPSED MINUTES
           SPEED (MPH) = ----------                MPM = ---------------
                         MPM FACTOR                       ELAPSED MILES


      MIN    SEC      MIN     SEC      MIN     SEC      MIN     SEC
      .01    0.6      .26    15.6      .51    30.6      .76    45.6
      .02    1.2      .27    16.2      .52    31.2      .77    46.2
      .03    1.8      .28    16.8      .53    31.8      .78    46.8
      .04    2.4      .29    17.4      .54    32.4      .79    47.4
      .05    3.0      .30    18.0      .55    33.0      .80    48.0
      .06    3.6      .31    18.6      .56    33.6      .81    48.6
      .07    4.2      .32    19.2      .57    34.2      .82    49.2
      .08    4.8      .33    19.8      .58    34.8      .83    49.8
      .083   5.0      .333   20.0      .583   35.0      .833   50.0
      .09    5.4      .34    20.4      .59    35.4      .84    50.4
      .10    6.0      .35    21.0      .60    36.0      .85    51.0
      .11    6.6      .36    21.6      .61    36.6      .86    51.6
      .12    7.2      .37    22.2      .62    37.2      .87    52.2
      .13    7.8      .38    22.8      .63    37.8      .88    52.8
      .14    8.4      .39    23.4      .64    38.4      .89    53.4
      .15    9.0      .40    24.0      .65    39.0      .90    54.0
      .16    9.6      .41    24.6      .66    39.6      .91    54.6
      .167  10.0      .417   25.0      .667   40.0      .917   55.0
      .17   10.2      .42    25.2      .67    40.2      .92    55.2
      .18   10.8      .43    25.8      .68    40.8      .93    55.8
      .19   11.4      .44    26.4      .69    41.4      .94    56.4
      .20   12.0      .45    27.0      .70    42.0      .95    57.0
      .21   12.6      .46    27.6      .71    42.6      .96    57.6
      .22   13.2      .47    28.2      .72    43.2      .97    58.2
      .23   13.8      .48    28.8      .73    43.8      .98    58.8
      .24   14.4      .49    29.4      .74    44.4      .99    59.4
      .25   15.0      .50    30.0      .75    45.0     1.00    60.0

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