Judging is via 2 synchronized clocks. At the start line, a clock displays the "official time". Cars are cleared to leave on the minute. Your personal time begins as the clock changes from XX:59 to XX:00, whether or not you actually leave is irrelevant. Your time ends when you cross the finish line laser. For example, if my start time was at 8:00:00 and my target speed was 180, my time would be the elapsed time between 8:00:00 and the instant my bumper broke the laser beam across the finish line 90 miles away, ideally at 8:30:00.0000.

The classes are governed with both minimum and maximum speeds, usually 20 under and 20 over target. Random radar stations enforce it and any violations are grounds for immediate DQ and possible ban from future events. My understanding is that the road was surveyed at the centerline and the guys with the really accurate odometers seem to come out nearly perfect.