Abstract: An apparatus for on demand limiting the value range of a parameter adjustment device comprises a knob for moving a regulating element (1), means for creating engagement between the knob and the regulating element (1), a first stop (3) fixed in relation to the device, a second stop (6) to cooperate with the first stop (3), a shim (5) having said second stop (6), and movable independently in relation to the regulating element (1), a spring (4) an end of which is fixed to the first stop (3) and the other end is fixed to the shim (5), and a pressure element (7) having a surface for frictionally engaging said shim, and fixed against rotation to said regulating element, and means for releasably engaging said surface with said shim.