Factual error: The morning after Leopold and Stuart travel to the present, the two of them are talking about why Leopold followed Stuart to the bridge. Leopold mentions that he was afraid Stuart might be Jack the Ripper, whose first murder was in 1888, twelve years after Leopold's time. (00:17:55)
Factual error: Leopold recognizes the telephone as the "talking telegraph" he saw at a fair "last year" in the scene where Stuart calls home from the hospital. The first public showing of the telephone was at Philadelphia Centennial Exposition which opened in May of 1876. (He is from April of 1876.) That aside, if he saw a talking telegraph in 1875, it would've been quite a feat because inventor Alexander Bell submitted his patent in 1876. (00:30:15)
Factual error: Otis elevator is called that because Elisha Otis invented the modern elevator in 1859, 17 years before the movie takes place. It had nothing to do with the Duke of Albany.