Continuity mistake: Near the end of the movie, the panel has JPE 1704 TKS showing, but when Joshua finds the launch code, CPE 1704 TKS is blinking on the screen.
Continuity mistake: During David Lightman's escape from the infirmary, notice the hands of the guard officer - he's wearing his gloves, and the next instant they have disappeared, and reappear in the next scene.
Continuity mistake: McKittrick asks David, whom he was going to Paris with. However, the reservation was made in Jennifer's name, not David's.
Continuity mistake: When David first talks to Joshua through the computer, Joshua types the word -mistakes- on the screen but two shots later, it is spelled mistak.
Continuity mistake: The tour group comes in and they trick the black lady into pressing the red "launch" button that displays the welcome on the screen. Just before she presses it she has a 35 mm camera hanging around her neck, but in the next shot of the group standing in front of the panel her camera is gone.
Continuity mistake: In the scene where Joshua is going through the possible strikes, the US strike was done first followed by USSR's strike. However, when you see the list of strikes and the results, USSR is listed before US.
Continuity mistake: When Matthew Broderick plays "Galaga" later in the movie, when Jennifer asks David to fix her grade again, there is a shot in which David has two lives remaining when his ship is destroyed, but in the next shot, the game has ended.
Continuity mistake: When David's father is pushing the dog down from the kitchen table, he has a knife in his left hand the whole time. The next shot however shows the knife no longer in his hand and him picking up the knife from the butter tub.
Continuity mistake: Towards the end when the NORAD door is closing, they keep showing it opened further from shot to shot in order to delay how quickly the door actually is closing vs. how slow it really would have had to move in order to allow David and Dr. Falken to actually have still made it in.
Continuity mistake: In the very beginning, when the Air Force brass land at SAC in the helicopter, they get into a 2 door Jeep Cherokee. After they enter the tunnel and stop to get out, they exit a 2 door Jeep Cherokee Chief - the wide wheel well model, not the standard one they first got into. (00:07:25 - 00:08:25)
Continuity mistake: When David and Jennifer leave Falken's house, it is fully dark out. When the helicopter is shown flying around to pick them up, the sky changes from fully dark to some twilight in the sky, depending on the angle shown.
Continuity mistake: In the scene towards the beginning of the movie when McKittrick, the General and others are discussing the problem that numerous missile commanders failed to launch their missiles because they believed the order to launch was not a test. As the camera shot goes back and forth on the actors in the room as they are talking, you'll notice McKittrick's hair goes back and forth from neat and combed to messy and disheveled.
Continuity mistake: When everyone is trying to get Joshua/WOPR to stand down from launching its own missiles, McKittrick's assistant Paul is standing with the rest of the group, but then there is a quick shot of Paul looking at the WOPR and then within seconds Paul is overheard saying "must be caught in a loop" as if he's standing beside everyone again.
Continuity mistake: The 1 minute 30 second countdown takes almost 2 minutes and 30 seconds, despite it being a continuous shot. And the last 10 seconds takes at least 13 seconds, despite each number being counted down out loud.
Continuity mistake: When Matthew Broderick is first at his computer the screen is large and has an external modem on top. Later there is a close up shot of the keyboard and the monitor. At this point the monitor is completely different and much smaller. Then shortly afterwards you can see the larger monitor again with the modem on top (behind Ally Sheedy) while it war dials numbers. Shortly after that, the monitor changes again. You can also see the changes with the color and the "side handles" used for carrying. I counted three different monitors being used.
Continuity mistake: When NORAD is waiting for the bombs to initially hit the bases, the animation of the inbound nukes is replayed multiple times showing the same approach towards Loring AFB.
Answer: The assistant to McKitrict explains that US is waiting to go back on DEFCON once the Russians do so.