Continuity mistake: When Luke and Leia are stopped in front of the pit, one stormtrooper arrives at the other side and shoots at them. Two others arrive later but in the following shot, there's only two stormtroopers, not three. One has disappeared and there's one dead on the floor that we have never seen dying. After that, the dead one disappears and two stormtroopers arrive again - it's the same shot as the beginning, only from another angle. Then, there's one that gets shot and falls in the pit and the dead stormtrooper reappears on the ground.Dr Wilson
Continuity mistake: When the Jawas arrive to sell the droids, Luke walks over to R5-D4 (the "R2 unit with a bad motivator"), and the droid is standing in front of R2-D2 on Artoo's left. In the next shot, the two droids are standing perfectly next to each other, and there are several Jawas around them that weren't there in the previous shot.
Continuity mistake: In the Detention Block, Han and Luke are in their stormtrooper outfits and are firing at the enemy. They go to a shot of Han then to Luke. Luke's white shoulder pads of his stormtrooper outfit are clearly missing, and you can see a black undergarment. They then go back to Han and then back to Luke again, where the shoulder pads are now back. (01:15:20)
Deliberate mistake: When Obi Wan deactivates the Death Star's force field, there's an electronic gauge going down and a sign in clear English with the word POWER - as we've seen in shuttles and other places, they don't use English. The studio decided it was better to show "power" and "tractor beam" in English so that the audience would know what Obi-Wan was doing. The lettering we see in Jedi doesn't really affect the plot, so it doesn't need to be English. Still doesn't really fit though. This is fixed on the DVD.