I don't understand- How is old Biff able to use the time machine if he doesn't know how it works?

didnt the delorean have labels on the numbers that said the time you left, the time your going to, and the current time. and if that was there then old biff could have just set the time machine for 1955 then drove not knowing the that 88 miles was the time travel speed.

Back to the Future II is full inconstancies. The thing has more holes than swiss cheese. Biff can work the time machine because no one really thought it through.

Doc is pretty absent-minded for such a genius, so i'm sure he made the controls not incredibly complicated so that he wouldn't forget. Plus, Marty was able to operate the machine, and he is not exactly a brainiac. Plus, Biff was probably not as dumb as his younger self, and since he lives in a future of flying cars, operating that sort of machinery is probably nothing new to him now.