Procedure

For every increase in pressure of one division from calibration, subtract two meters from a 5000-m course.

1. One division refers to that on outer scale of Accu-Gage (20 kPa).
2. For one division decrease, add two meters.

Discussion

I formulated the above simplified procedure in response to recent comments that the method was too difficult to understand, and that a tire history would have to be accumulated before it could be applied. Error of simplification is probably very small compared with other errors involved in measurement.
I do not like the use of meters in course measurement because it is unsophisticated and unnecessarily complicated. However, I realize I have not convinced anyone else of these facts, and the quoting of meters in the above procedure does allow all measurers to readily incorporate pressure monitoring into their own traditional procedure. Ideally pressure readings should be taken at the mid-point of rides, but for 5-km courses it probably makes little difference if they are taken at the beginning or the end.
Measurers can easily test the procedure by riding a calibration course early in the day and riding the same number of counts over the course a few hours later. If the course is 400 meters and pressure is one division higher on the second ride, it will end 16 cm (200x0.4/5) beyond the end of the course.
Original Post

Any measurer working alone, with the same bike, to do the two measurements, can get by with any system of units he wishes. He can use revolutions, counts, feet, meters, miles – whatever fits his inclinations.

When he works with another measurer, it is necessary to use a common system of units. Otherwise there is no way to compare the measurements. If I am using revolutions and Jack is using a Jones counter, how do we compare the result of the two measurements? Only by converting to a common standard of length.

Two meters in a 5k should be easily understood by all. It is useful no matter what the measurer is using to count the revolutions of his wheel.

I don’t agree that using meters lacks sophistication. It is the use of counts or revolutions that is imprecise – all bikes will differ as to the value of a count or a revolution, but meters, kilometers, feet or miles must be used in expressing lengths. Anything else leads to puzzlement.
Pete:
I am glad at least we agree that a measurer working on his own does not need to convert his measurements to standard units such as meters.

However the same applies to two measurers working together with different bikes and measuring devices. For example, suppose Jack and Jill agree to share the work in certifying a 15-km course. Jack does one measurement at 50 deg using a Jones meter and marks his finish. A week later, when the temperature is 75 deg, Jill using a Protégé calculates she needs to ride 7185.75 rev, but comes to Jack’s mark at 7184.75 rev. Therefore Jill’s measurement fixes the course length as Jack’s finish is 0.0139% (1x100/7185.75) short of Jill’s. Here we have a precise comparison between the two rides without involving meters.
Most measurers seem to express their split distances in meters to as much as six decimal places. I know this is easy using a spreadsheet, but I cannot imagine what purpose it serves other than to reduce clarity.
Dear Neville,

The end result of all our measuring is a statement of length. Your supposed simplification is wordy and clumsy.

What could be more simple than to say:
Jack's measurement of the course = 15000 meters
Jill's measurement of the course = 14997.9 meters?

Opinions of others on this subject are welcome.
Pete:
The most fundamental way of comparing the two rides is not the numbers in meters you give but the percentage difference. Also, the latter is required by RRTC to show that it is less than 0.08%.
The thing that is most inelegant about the method of working in meters is that it requires the measurer to take out a measuring tape and make a course adjustment at the end.
I agree with Neville that converting counts to meters is not necessary to determine whether two measurements agree within 0.08%, if the two working constants are the same. The measurer can convert counts to meters later, when he fills out the forms. However, when I measure a half marathon, I calibrate my bicycle between the two rides of the half marathon route. My working constants are usually different, so I need to convert counts to meters to determine whether my two measurements agree within 0.08%.

In Neville's Jack and Jill example above Jill's measurement may not fix the course length. She needs to calibrate her bicycle again, after making her measurement. Then she may need to adjust the course length.

Using a steel tape to make the final adjustment to a course is easy for a measurer to do and easy for a certifier to understand. A steel tape doesn't need to be calibrated. A bicycle does. Using a bicycle to make the final adjustment to a course could be complicated. What if the constant of the day is not the same as the working constant? Would a measurer need to check his bicycle on a calibration course after making his supposedly final adjustment to the race course?

Dale Summers
Dale:
I did not make it perfectly clear in my story above that Jack and Jill were using totally different calibration factors (working constants): Jack had a 700 tire at 80 psi with the temperature at 50 deg while Jill had a 27-in tire at 100 psi with the temperature at 75 deg. Jill did not even know what Jack’s calibration factor was at the time of her measurement. Nevertheless, she was able to finalize the course and calculate a precise % difference for the two measurements without any conversion to meters or using a measuring tape.

Your case with the two half-marathon rides is entirely analogous. Just pretend you are Jack on the first ride and Jill on the second and you will not have to make any conversions to meters.

I also forgot to add that Jill was using pressure monitoring and so was assured that she would not have to make a course final adjustment. She simply stopped halfway through her ride, read her pressure gauge, and using the formula in blue at the top of this topic, calculated that she would need 7185.75 rev to finish her ride.

To get similar assurance of not having to make a course adjustment by using the postcalibration method instead of pressure monitoring, she would have had to take the more inconvenient measure of making all her measurements during part of the day in which temperatures were steadily rising. Nevertheless, if her postcalibration factor still turned out to be higher than her precalibration, she would have had to add to her course ride. This gets impractical if her calibration course is say 100 miles away, and she would have to contact say the race director and get him to add to the course with a measuring tape. Of course, one of the reasons I devised pressure monitoring was to totally avoid these difficulties with postcalibration.