Doc holds up the now unsynchronized stopwatches.
Light Emitting Diode stopwatches were used by Emmett Brown in his initial time travel experiment. They were both synchronized until one — that worn by Einstein in the DeLorean time machine — traveled one minute into the future, skipping over the minute that the other watch experienced.
Behind the scenes
- Doc and Einstein wore matching stopwatches with liquid-crystal displays, except during the two scenes in which he compares the watches before and after the experiment. Apparently, the time on these stopwatches was too dark to seen on-screen as the script required, so these two scenes were refilmed with LED stopwatches.