Back To The Future Part I
Tower Clock turns 10:01pm twice during the storm.
Marty sets the Delorian to return to 1985 at 1:24am, but when he
arrives the clock on the dashboard says 1:20am instead.
In the cafe George stares at Marty when he suggests Goldie
will become Mayor. He then looks at Goldie, who was standing behind him, without turning around.
Einstein's time jump
lasts about 70 seconds but the stopwatch is only sixty seconds behind "Doc's".
The Delorian is clean when it materialises
after Einstein's journey is complete, but when "Doc" opens the door a moment later the car is packed in ice.
When "Doc" returns to 1985 at the end
of the film, the Delorian doesn't freeze over at all on re-entry.
Back To The Future Part II
The ladder above the stage at the school dance wasn't there in
the first film.
Reality fails to change after Old Biff goes back in time (surely he should have returned to a future
where he was ruler of Hill Valley...?).
Biff's car doesn't have a rear-view mirror in the Garage, it does on the road.
Scenes from the first movie are out of synch when re-filmed here.
The thunderstorm stops dead after the Delorian
gets struck by lightning, but it's still going when the lightning strikes the clock tower.
Marty's cap disappears
after he leaves it on top of the video game machine.
Griff's "pit-bull" hover board smashes through the clock-tower
window, but the kid on the other side of the lake has it a few seconds later.
"Doc" says if anyone encounters his
future/past self it will cause a paradox that will destroy the Universe, or they will pass out. Later, relative time, Biff
from the 1950's encounters his future self from 2015 and nothing happens.
When Marty is dicing with death hoverboarding
on the trunk of Biff's car, the book couldn't have landed on the windscreen from the angle it appears to.
To The Future Part III
If the steam engine is travelling
at about 85 miles per hour, it must surely be moving faster than the hover-board's maximum speed. And yet, after "Doc" catches
Clara, the hover-board actually ACCELERATES and appears to overtake the Delorian.
The Old "Doc" in 1885 has no memory
of dressing Marty in the silly cowboy outfit, nor of seeing his own gravestone.
The appropriate components for building
a flux capacitor weren't invented until 1947, according to "Doc's" letter, but "Doc" manages to build a flux capacitor and
fits it into a steam train before the turn of the 20th century.