hi, im a real racer. and i my car i have a mychron, and it has an option wich can gives you this times:
Best Theoretical Lap time
This lap time is calculated adding all best split times you made during your run on the same track. This Lap time is only theoretical, because is made calculating the best recorded split times of different laps.
Best Rolling Lap Time
This Lap time is obtained adding all best consecutive split times you really obtained. This means that this lap can also not begin at start finish line nor ending there.