Text in force at 25-153: from 25-72, effective 20 Aug 1990.
Cockpit control knobs must conform to the general shapes (but not necessarily the exact sizes or specific proportions) in the following figure: FLAP CONTROL KNOB LANDING GEAR CONTROL KNOB MIXTURE CONTROL KNOB SUPERCHARGER CONTROL KNOB [POWER OR THRUST KNOB] PROPELLER CONTROL KNOB
55 FR 29779 · Source