LOL! Reminds me of a story my father told me. When he was a young man (he's almost 90 now), there was a siren that sounded in town at noon each day. There was also a military academy which fired off a canon at a certain time each day.

He asked the people city officials how they knew when to sound the siren and they said they set their clocks by when the academy fired off their canon. When he asked the people at the academy how they knew the exact time to fire the canon, they said they set their clocks by the siren!

Actually, I think that is what often happens with these measurements for races in a sense. Someone measures it somehow - no one probably even knows how they did it - but from then on that route is consider to be "correct". And if they alter the course slightly - maybe start it a mile earlier, but want to go the same distance, they simply measure a mile from the old ending point. So any errors are still there even with a changed course.