When possible, controls should be differentiated by shape.
Additional Information:
The shapes of conventional controls should be identifiable both visually and tactually to facilitate "blind" manipulation. When shape coding is used: (1) The coded feature should not interfere with ease of control manipulation; (2) Shapes should be identifiable by the hand regardless of the position and orientation of the control knob or handle; (3) Shapes should be tactually identifiable when gloves are worn; (4) A sufficient number of identifiable shapes should be provided to cover the expected number of controls that require tactual identification; (5) Shape-coded knobs and handles should be positively and non- reversibly attached to their shafts to preclude incorrect attachment when replacement is required; and (6) Shapes should be associated with or resemble control function, and not alternate functions.