Croke Parkings!


You should have keyed your parking bay number into the machine before you selected the number of hours and paid.

Q-park's system lets them see which bays are paid or expired and they clamp if necessary.
 
(In Germany, they don't have any uniform, but merely wave their ID in your face. Makes it harder for ticket dodgers to spot them boarding and hop off before the doors shut)
My experience of the ticket checkers in Budapest was similar.