Fantastique clock

Any hour from 1 to 12 is secretly chosen by a spectator. On turning over the clock one sees a jumbled mess of letters. These are tapped by the magician one at a time. When the spectator asks the magician to stop counting, he puts a matchstick through the appropriate hole and on turning the clock over it is seen that the magician has stopped on the hour chosen by the spectator. Complete with instructions.