When an indication of position is desirable, it should allow the user to easily recognize the position.
Additional Information:
The pointer configurations shown in bottom of Figure 3.7 may be used. Where more accuracy is required, a line should be engraved (and filled with contrasting pigment) both on top and down the side of the pointer, as shown on the knob at the bottom of the figure.
Figure 3.10 Recommended dimensions for rotary controls with finger stops and skirts.