In initial shots, the time machine's computer is a Commodore 64 with a 1541 floppy disk drive, which is also generates the screens and provides voice synthesis. Later on, it changes into a Commodore Amiga 2000, complete with separate keyboard, which was previously in Nick's living room.
Nick rests against a tree while he escapes through the woods. When he gets up, his butt is covered with mud and leaves. In the next scene, his butt is relatively clean.
The crashed version of Nick's plane from the future is yellow, but at all other times it is very obviously red. This does not prevent Nick from immediately identifying the crashed yellow plane as his own.
Robertson's Uzi vanishes and reappears as he flees through the woods.
In the opening sequence, Nick reaches into the plane with his left hand to retrieve the floppy disk. He retrieves the disk with his right hand, but when Nick pulls his hand back out, the disk isn't there.
Nick steals a car to escape the Gen-Cor guards. The car crashes into a pile of bikes and flips over on its side. As it tips over, the device used to make the car flip sticks out of the bottom of the vehicle.
When the two Nicks are on-screen together, the different lighting and sky color make the seam in the split-screen effect obvious.
In 1777, the American flag had 13 stars, not 50.
In 1777, modern buildings and electrical poles are in clear sight while Nick crawls all over the plane.
The 1950s diner has plastic soda cups.
In the 1950s diner parking lot, a lot of cars have "antique" license plates.
When J.K. tries to escape with Nick on the wing, various trucks and cars are visible on the ground.
When Nick first phones GenCorp, a lighting canopy is visible in the mirror.
J.K. follows Nick back in time to the morning of Sept. 24, 1991, even though he has no way of knowing where Nick was going.
When J.K. and Nick arrive in 1777, the other Nick and Lisa have convinced the colonists to attack J.K.. Nick and Lisa have never met J.K. or anyone who would know that he's the bad guy.
No explanation is ever granted to how the aircraft lands in different times. Aircraft must request permission to land, log where they came from and where they are going. This should still be happening in 2041, and would have caused some raised eyebrows in 1957 with the future aircraft. Not to mention there were no runways in 1777, so landing and taking off would have been dangerous.
When Nick confronts J.K. Robertson about using the transport as a weapon, a boom mic is reflected in the large mirror in J.K.'s office.
Matthew Paul speculates that if he put $100 in the bank then traveled 100 years into the future, "the interest alone would make you a millionaire." He'd have to deposit much more than $100 to get rich off the interest. No bank offers an interest rate that would yield $1 million of interest from $100, even after 100 years.