Descriptions and operation: Tachometer: Notes
WARNING: This page is about a different car, the 2006 Saab 9-5. However, it is still accessible from the selected car via links, so may be relevant.
The main instrument is fitted with an electronic tachometer. The engine control module continuously sends information on the engine speed to the bus.
The tachometer is controlled by a stepper motor. The stepper motor is controlled by voltage pulses from the main instrument control module. At speeds below 1100 rpm (idling range), the display is "damped" to give a more stable speed display.