In the original Back to the Future when Marty is trying to get back to 1985, Doc puts an alarm clock on the dashboard of the DeLorean and tells Marty:
"I've calculated the distance and wind resistance retroactive from the moment the lightning strikes. When this alarm goes off you hit the gas."
Moments before the alarm goes off, the DeLorean's engine stops and Marty struggles to get it to start again. While he struggles with it the alarm clock rings. When the engine eventually starts Marty then starts to drive the car and he is successful to travelling back to 1985. Because he started a few seconds late due to the engine trouble, were the Doc's calculations incorrect by a few seconds?