Rotating knob controls for different types of control actions should be distinguishable by sight and touch and not easily confused with each other.
Additional Information:
Figure 3.7 gives examples of suitable knob designs developed for three major classes of knobs, each class intended for a different purpose: multiple rotation, fractional rotation, and detent positioning. General guidelines for coding controls (including shape coding) are given in Section 3.1.2, Coding of Controls.
Figure 3.7 Shape-coded rotary controls.