A device (10) having a plurality of rotatable hand-operable knobs (36), rotation of which changes respective parameters of the device (10). Each knob (36) has a toothed wheel (90, 92, 93) fixed relative thereto, and rotatable therewith. The wheels (90, 92, 93) have respective clicker portions (94) engaging the teeth thereof to define respective different positions of the wheels (90, 92, 93), in which the clicker portions (94) are integral with one and the same part (96).
