There were several attempts to make digital clocks out of analog voltmeters. They work great and look pretty good. But this one beats all expectations, because here an analog clock is used to measure voltage. This is really not practical way of doing this, bus someone had to do this.
Practically this solution is very simple – a stepper motor turns adjustment knob according to measured voltage value. If its 1V then clock shows 1 o’clock and so on. So voltage range is 12VDC. The brain behind this is a PICAXE 18N2 microcontroller which reads voltage value and controls stepper motor using L293D motor driver IC.