An adjustment drive for an adjustable spacing comb for a hair cutting appliance includes an actuator configured to actuate a movable comb portion of the adjustable spacing comb with respect to a blade set of the hair cutting appliance, and a drivetrain for coupling the actuator and the movable comb portion. The drivetrain includes a reduction gear unit and a location detection unit having a rotary encoder which is coupled to an output shaft of the reduction gear unit.