Last weekend another measurer and I measured a long course in the local area. Because of its length, we elected to set a calibration course approximately midway. We measured approximately the first half of the race course, re-calibrated, and proceeded to finish the course measurement.
When we sat down to calculate the course length, it became apparent that his splits over the first half of the course were consistently shorter than mine. Over the second half, though, we were within a meter.
We compared calibration data. On the mid-calibration and the post-calibration, our numbers were consistent; his counts over the 300 meter course averaged 1.75 to 2 counts less than mine. On the pre-cal, though, they were almost the same. My pre-calibration counts were within 1, but his varied as much as 5 from highest to lowest. His counts on the other two calibrations were much more consistent with each other.
I remember that there was once a standard regarding how close calibration rides needed to be to each other, so I went back to some of my old manuals. There it was, in the original 1985 manual, it stated that calibration rides should be within 0.07% of each other. That verbiage was missing from later manuals.
I've pretty much always held to that standard. I generally only calibrate over 300 meters now, but I always make sure I have four rides, including two in each direction, that are within 2 counts of each other. I adjust that on the rare occasion that I use a different length course. If you can't ride four rides within two counts, something is wrong and you need to attend to it.
We were eventually able to make things work using average constants, but I learned a lesson. Always make sure your calibration numbers agree with each other. If they don't agree, keep riding the calibration course until they do, whether the manual says you have to or not. There are a lot of things that can make two measurement rides not agree with each other. Don't make inconsistent calibrating be one of them.
We allow the use of the average constant. This can be a help sometimes when data must be reconciled. The larger constant does not give as good a comparison of two riders' data as does the average.
The average can also save aggravation. I measured a course a few weeks ago, on two different days. My second ride was the best. However, I made a miscalculation on site and left without making a 2 meter final adjustment.
When writing up the measurement at home I found that if I used the average constant, the measurement results came out a bit longer (as they always will, using the average), which put the final distance in the OK range. This saved me a 40 mile round trip to make the adjustment.
Thanks, gentlemen. This discussion has been helpful.
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