not much can stop them, i know a school which i wont name that allows people to talk, overlooks many things, they also dont have clocks which tell the exact time, i had a countdown timer which counts time to the second, and i found on one exam they said we had 5 minutes remaining when we only had 3 but then stopped us about a minute earlier, and another exam they stopped us about 1.5 minutes after time, which actualy can make a difference..
what i find really annoying though is how the supervisors never start on time, its a little thing and they always give us made up time, but it is hard for me to calculate how much time i spend on each qstn wen they start at 12:08 as oppose to 12:00