In reply to alan wilson:
I suspect that the tolerance/variance from track is proportional to the length of the route.
You quite often find it has skipped short sections
Also I did a ride recently where it told me I was 2nd on a segment. Whoopee I thought, I wasn't even trying. Except it turns out to be 2nd of 2, on a segment that I must have ridden 20 times in the last year.
More to the point it didn't give me a time for the longer segment that I use as indication of how well I'm going.