Originally Posted by Gatwick Alan

Thats what i wondered, i assume they know because you hand in your i94w which is attached to your ticket when you board the plane. If thats the case what are the machines for? On some occasions the i94w has been taken at the check-in desk and sometimes ive gone back outside for a cigarette after going through security, then gone back through again. I could easily have used the machine, then gone outside again.It just doesnt make sense.