Other mistake: Why didn't Falken just call NORAD instead of going 1400 miles? NORAD in Colorado Springs, Colorado, U.S. to Goose Island, Oregon is far (1,388.5 mi). Robinson R22 has a maximum speed of approximately 115 miles per hour. The R22 typically has a maximum range of around 200 to 240 nautical miles with standard fuel tanks. It would have to refuel 8 times, making that long 16+ hour trip before the wargame ended, is impossible (not to mention arriving 'just in time').
Factual error: When Joshua/WOPR calls David back, the sound David hears on the phone not only isn't what modems actually sounded like, but in reality, the answering modem makes the initial sound to start communications, not the calling modem. The calling modem remains quiet until it hears what start tone the answering side answers with so it can start negotiating baud rate, encoding method (FSK vs PSK), etc.
Other mistake: When David and his dad are sitting at the dining table, dad butters his bread to roll his corn on the cob. You can see that the butter melts on the corn and bread, but then he bites into the corn and finds that it is raw. Raw means uncooked and the cob would be cold, therefore the butter wouldn't melt.
Other mistake: When David was having his computer dial all the numbers in Sunnyvale, he pulled up the list of numbers already dialled, and there are numbers with the prefix '936', but before he pulled up the list, when the computer was dialling the numbers, the 936 prefix was on the far right hand side. No numbers with the 936 prefix were dialled yet, so they could not have been on the list.
Revealing mistake: When Joshua/WOPR is trying to figure out the launch code at the end of the movie it picks the "1" out of the 1704 twice.
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.
Factual error: As the computer repeatedly tries different bombing strategies, all resulting in "WINNER : NONE", one of the strategies it lists misspells "Israel" as "Isreal" and "Palestinian" as "Palistinian."
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.
Factual error: In the first scene with the computer (when Ally Sheedy visits) Matthew Broderick puts the handset on to the modem coupler with the cord toward him, then pushes the button on the modem which is facing him. A shortly while later he is at the computer and he puts the handset backwards with the cord away from him and pushes the button which is still facing towards him. The modem would not have worked properly, since it needs to send and receive through the respective ear and mouth pieces.
Other mistake: When David first logs into the system after finding the right password, it shows a phone # beginning with the prefix 936. The only problem was that earlier when his computer was dialing numbers, he had not gotten to 936 yet. That was the 4th prefix and he only got through the first 3. There is no way he could have dialed that number with his computer program.
Revealing mistake: When David begins to play against the WOPR computer, the images on the war room screens show various tactical movements by other countries. These are the same images shown the first time the war room is seen.
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.