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 Larger constant vs. average constant vs. something in between

 posted 06 September 2010 23:25
This past Saturday I measured a half marathon course. The course started out with most of a loop, went out for more than five miles, had a loop at the other end, then came back the same way it went out (on the other side of the path), then closed the initial loop, finishing at the start.

The original measurement yielded a length of 21135.23 meters using the pre-cal (larger) constant so the race director and I found a couple of alternate routes that would shorten the course. measured them, pasted them in, and ended up with a course that was 21090.53 using the larger constant, and would be 21099.48 using the average constant. I recalibrated, rode the course again, and ended up with course lengths of 21090.80 using the larger (pre) constant and 21098.90 using the average constant from the last two calibrations.

Here's the question: Since it is entirely legitimate to calculate the length of the course using the larger constant, and it is entirely legitimate to calculate the length of the course using the average constant, does it then follow that it is entirely legitimate to calculate it using ANY constant between them?

If so, I have a 21097.5 meter course. If not, I have one that's a little long. Either way it works- but since there's obviously a number in the range that gives me exactly what I want, I thought it was worth posing the question to the group.

Jay Wight

 Posts: 208 | Location: Hoffman Estates, Illinois, USA | Registered: 25 October 2004 IP

 posted 07 September 2010 06:34 Hide Post
This looks like a legitimate approach to me.

However, it's always a mistake to think that you have arrived at the exact, correct length of the course. What you wind up with is a course with the correct nominal length, which will exceed the desired length by about the amount of the SCPF.

You'll have two marks on the road, and you'll have a variety of estimates of the length between them. But the course will be OK.

Exact measurement will forever elude us.

This message has been edited. Last edited by: Pete Riegel,

 Posts: 1756 | Location: Columbus, Ohio, USA | Registered: 23 October 2004 IP