[JP1738]

Speaking of the 594' mark, does anybody know why it's 66ft? If the only thing it does is serve as a reference time to calculate speed based on the time it takes to traverse that span, why is it 66 feet? Why not 10 or 20? Seems arbitrary to me.

66ft would be 1/10 of an 1/8th mile and 1/20 of a 1/4 mile, but you could easily use any increment you want. I don't know why the people who invented timing systems used that distance and I've never been able to see why in all my research.