Mondial QV odometer

The odometer recorded less mileage than actual driving distance when I bought my car. After a while it stopped working. The speedometer is working fine. I have seen on the wiring diagram that there are 2 leads from the sensor at the gear box. One lead to the speedometer that branch off to the odometer and one lead directly to the odometer. I have delivered the odometer to a workshop for repair. They ask me about what kind of signal the sensor deliver. Is it variable voltage, is it a pulse, or what is it?