Pete:
I should like to respond to the points you raised in your last post.
(1) Calibration values change constantly during a ride, as portions of the course may be in hot sun, while others may be shaded. If the pressure in the tire is adjusted to match that of the pre-calibration, it may be necessary to be sure that the conditions are the same.
I am not quite clear as to what you mean here. However, my results so far seem to indicate that it can be cool and shady at the calibration and hot and sunny at the race-course measurement, but if the same pressure is used, the calibration constant changes little.
(2) While it may be possible to measure, say, a 5 km course in 20 minutes, and while the pressure may stay relatively constant during that time, it is more common for a 5 km measurement to take a few hours, as it rarely comes out right the first time, and requires adjustment. During this time the pressure is going to change. What is to be done? Take a reading every half hour, and release air or pump it in to maintain a constant pressure? This is risky business.
It should only be necessary to monitor pressure during the few minutes spent on the critical rides not on the many hours usually spent at the site.
(3) If the tire pressure is not adjusted during the measurement, but is checked afterward, it will be found to be different than at the start. What is to be done with this information? If my tire pressure is 125 at the start and 122 at the end, what do I do about it?
I think this is a minor detail that would be easy to get everybody’s agreement on. Any increase in pressure could be ignored as this would give a longer course. An adjustment for any decrease could be made by adding 0.5 m/psi for a 5K. In the example you give (which would be rather extreme for a 5K) the average fall would be 1.5 psi and 0.75 m would be added.
Given the above I can see no reason why the pressure method is in any way easier or better than the method we use now. The fact that it can be used by a knowledgeable individual with custom pressure-measurement equipment does not make it a better method. The precal-measure-postcal method frees the measurer from any concern about his tire pressure and allows him to focus on the measurement itself. This makes mistakes less likely.
The traditional method does not free me from concern that measurements taken as temperatures peak mean an overly long course.
As the sole benefit of the pressure method is to avoid postcalibration I believe the cure is worse than the disease.
I see the following benefits of pressure monitoring:
(i) Improved accuracy.
(ii) Post-calibration not needed.
(iii) A temporary calibration course does not have to be set up.
(iv) Frequent recalibrations during course measurement not needed.
(v) Return to the race site to make adjustments in the measurements not needed.
(vi) Early alert of a slow leak in the tire so less wasted efforts.
(vii) Temperature measurements not needed.
(viii) Easier scheduling of measurements (eg do not have to get back for post-calibration before dark and rapid drop in temperature).
(ix) Calculations usually simplified.
(x) Tire puncture during measurement just a minor problem.