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In my role as an IAAF/AIMS area administrator, I have received a measurement report for approval. The pre calibration was done at 8am with temperature of 29C and post calibration was done at 5pm at 30C. WC = 11382 and FC = 11428. The measurer has made no comment or suggestion on why the post cal is 46 counts higher than the pre cal. I have gone back to him and asked for more information as I suspect a slow leak or, indeed, something more sinister. To date I've had no response.

This is an IAAF/AIMS measurement and measurers almost always take the average of the WC and FC to calculate the Constant for the Day. This has been done in this case to adjust the course.

Re-measurement of the course prior to the race is probably not an option (race in one country, measurer in another country). Depending on any answers from the measurer, my plan is to use the WC as the Constant for the Day and ask that the marathon course be lengthened by (46/2 x 42.195) 970 counts (approx 85m).

Any other thoughts? Has anyone seen such a large calibration variation with minimal temperature change?

Dave Cundy
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The difference of 46 counts per kilometer between the pre and post calibrations is much greater than I have ever had measuring. If I experienced this measuring, I would assume something was wrong. I would discard my measurements, check my bicycle and start over.
The time from 8 a.m. to 5 p.m. is much greater than I have ever allowed between pre and post calibration rides. When I have bicycled a half marathon for certification twice in a day, I have calibrated my bicycle between the two rides. That is three calibration rides; but if I have a flat tire the second time bicycling the half marathon, I wouldn't loose the first measurement. I can bicycle a 10 K fast enough to do it twice between pre and post calibrations.

I would use the larger of the WC and FC or use the average of the two.

Dale Summers
My guess is that a slow leak occurred, and I agree with your use of the larger as the day's constant. I suppose some incredibly bad postcal riding could have occurred, but if all four rides agreed this probably didn't happen.

I always felt hampered by the need to hurry when doing foreign AIMS measurements. One day is enough to do the job only if the person who laid out the course did it right, and this hardly ever happened for me. You do the measurement, and do your best to live with the result.

A marathon measurement near home generally takes me four or five days to get everything right, and the AIMS travelers rarely have that kind of time available, or can get access to the course.
Thanks for the various input. With further delving a number of additional issues arose with this measurement. In the end, I recommended the use of the higher calibration (finish constant). The courses (a marathon, half and 10km were measured in the one day, hence the long gap between pre and post calibrations) have been extended by the appropriate amounts.

I did discover that an inexperienced local measurer also joined in the exercise. This person had been trained by me at an IAAF RDC seminar in Jakarta in May. At first I thought his data would be a great help, particularly as his pre and post calibrations were almost identical. However he measured the courses to be significantly longer than the official measurer. After further examination and more questioning, I discovered I couldn't rely on his data as it would seem that he was at times distracted and didn't always follow the shortest possible route.

I approved these courses for just the one year and will insist that they be re-measured prior to the 2005 event.

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