i made a wall clock from an instrument cluster of a Mercedes-Benz SL-class. I'm using the speedometer to display hours (e.g. 70 km/h = 7 hours) and the tachometer to display minutes (5500 rpm = 55 minutes). The stepper motors of the instrument cluster are connected to a MotorShield which sits on top of an Arduino Diecimilia. The Arduino also decodes the time signal which is received by an external longwave time-signal receiver.