Factual error: Number 6 wakes up to find the Village deserted, but the central plaza fountain is still running - until he looks at it from the bell tower, when it's suddenly off. The Village fountains never appeared to be on timers (they were always on, day and night), and no one is there to turn the water off, yet it's somehow still off when Number 6 returns at the end.
Factual error: The truck transporting Number 6 and Nadia drives on the left side of the road. Fine for England, where the scene was shot - but they're supposed to be in Poland, where everyone drives on the right.
The General - S1-E6
Factual error: When Number 6 types "WHY?" on the typewriter, the sheet of paper comes out with the word centered on the page. But the typewriter's carriage was pushed all the way to one end, so the word couldn't possibly have wound up in the page center.
Factual error: Alison's Polaroid pictures develop themselves instantly. (In reality, you had to wait just over a minute before separating the developer sheet and finished photograph.) She also leaves the same flash bulb in when she takes a second picture - and it flashes again.
Factual error: Several of the chess moves called out over the loudspeaker are not possible with the players in their current positions. The Queen, for instance, is ordered to King three while in her starting position (can't be done). The "Knight to Knight's Bishop three" move is also impossible. When she is free to move to King three, though, the Queen goes there twice - without moving anywhere else in between.
Answer: It's even more obvious than you think, you know who number 1 is in the very first episode. When 2 replies to the question "who is #1?" Change the way he answers from you are number one (in the monotone or accented answer to, "You are, number 6. The comma gives you the answer. #6 is #1. It's the tone of the answer.