So you think you've missed a lap?

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Why computer race control systems -

1. Don't add a lap even if you go through on the wrong lane.

2. Don't always give an accurate fastest lap

Computer race control packages will generally time each lap and the good ones have an adjustable "hold off" facility to prevent double counting. This "hold off" (different packages have other names for a similar facility) is sometimes misunderstood, so I’ll try and explain what it does.

The hold off will not allow another lap to count for a preset length of time once one lap has counted. The race controller can change the hold off time, typically you’d only do this between classes. So if the fastest lap in a class is around 4.8 seconds you could set the hold off to 4 seconds, if fastest lap in another class is around 6.8 seconds you could set the hold off to 6 seconds. To explain what this does look at the diagram. This shows an example of a car " 1" lapping in its own lane, with every lap taking exactly 5 seconds. The hold off time is set to 4 seconds. Starting from the left hand side, the race starts and after 5 seconds car 1 clocks up its first lap, which the computer correctly shows car " 1" on lap 1 with a time of 5 seconds. The hold off is then set, so the counters won’t record another lap for the next 4 seconds. Thus when car " 2" gets in the wrong lane, and goes through lane 1 counters after 7.5 seconds the computer correctly ignores it and continues to shows car " 1" on lap 1. (Note car 2 will have missed a lap because it didn’t go through its own lane counter). 10 seconds after the start car " 1" clocks up its second lap, and the computer correctly shows car " 1" on lap 2 with a lap time of 5 seconds. The hold off is again set, so the counters won’t record another lap for the next 4 seconds (from 10 to 14 seconds from the start). When car " 2" gets in the wrong lane again, and goes through lane 1 counters 14.2 seconds after the start the computer incorrectly shows car " 1" on lap 3 with an incorrect lap time of 4.2 seconds. The hold off is again set, so the counters won’t record another lap for the next 4 seconds (from 14.2 to 18.2 seconds from the start). 15 seconds after the start car " 1" completes its third lap, and the computer ignores it so it now correctly shows car 1 on lap 3 but the lap time for lap 3 is incorrectly recorded as 4.2 seconds. 20 seconds after the start car " 1" completes its fourth lap, and the computer correctly shows car " 1" on lap 4 with an incorrect time of 5.8 seconds. The hold off is again set, so the counters won’t record another lap for the next 4 seconds (from 20 to 24 seconds from the start).

This is the best a computer system can do to cope with cars that don’t stay in their own lane. What does this this tell us (apart from cars in the wrong lane are a b*** nuisance to all concerned)?

The hold off time should be set only slightly below the fastest possible lap.

Extra laps are not recorded when a car passes over in the wrong lane (So when blue lane cars goes trough on red lane in the middle of a race and the marshal shouts one off red one on blue, don’t take one off red!)

When a car misses its own counter strip, the computer has no way of knowing its done a lap. So when the blue lane car goes through on red lane and the marshal shouts "one off red one on blue", the race controller should add one on blue. Some race control systems do indicate a possible missing lap, so the race controller can decide if a lap is to be added on. What the computer is actually doing is showing that a lap was over twice as long as normal. When a car misses a lap, the time between registering on its own lap counter will be the time taken for the two laps plus the time it takes a marshal to put it back in the right lane - obviously at least twice as much as two normal laps.

The fastest lap recorded by the computer is usually right, but cannot be absolutely trusted unless you are sure that no cars have gone through on the wrong lane during that race.

If a car goes through the counters in the wrong lane at the end of the race, it is just possible that an extra lap has been recorded. The marshal should immediately tell the race controller that a car has gone through on the wrong lane, and it should be fairly easy to sort out if an extra lap has been gained from the last lap time on the screen and the position of the cars on the track.

Computer Race control systems are there to make a good race controllers job easier - not to replace him (or her). There are lots of things a race controller still needs to do even with the best computer system. For example, it is very helpful for the Race controller to let the driver / marshal know that they are dealing with the extra lap. Race controllers often say something like "OK one on red" so the driver / marshal know it's been attended to. Often, if they get no response from race control, they will (quite reasonably) assume the race controller didn't hear, and repeat it with increasing loudness until it is acknowledged.

Chris Frost

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