The problem with using the Sport Chrono for any real lap timing is that it requires human input, and worse yet, from the driver.
If you're trying to get any accurate lap times, you cannot do it in this manner. Especially silly is the fact that the timer measures into the hundredths.
The fact that it take input from a driver is the most useless part about it. If you're driving 9/10ths or 10/10ths out there on a track, the last thing I want anyone doing is fiddling around with a lap timer. You're supposed to be concentrating on driving. In a hobby/sport where improvement is measured in hundredths of a second, you don't have time or energy to waste on activities such as these.
Anyone who's really trying to record their laptimes will be racing with a transponder on their car that works with a lap timing system that can accurately tell you your lap times--yes to the hundredths. At the very worst, you'll have someone standing at a fixed point on the track with a stopwatch, timing you against a perpendicular point as you pass it.
The Sport Chrono is useful for timing how long your trip to the grocery store took, or how long you got delayed by rush hour traffic, and that's about it.
