The marks on the front panel around a control such as a knob or slider, which provide a visual reference as to the control's current setting, are known as index marks. (Also sometimes called tick marks or scale marks.) The way this is often done is: Common single-turn potentiometers have a 300-degree range of rotation. The index will have 11 equally spaced marks, starting from the lower left of the knob's diameter and going around clockwise to the lower right. These marks may or may not be labeled by numbers 0 to 10. If so, the 11 major index marks often have five smaller marks in between each, which provides a "one tenth" resolution to the value, such that if the knob's pointer is pointing at the third minor mark clockwise from the 1 major mark, then the knob can be said to be set to the value 1.6. If the major marks are not labeled, they can be viewed as positions on a clock face; the most counterclockwise position is "7 o'clock" and the most clockwise is "5 o'clock". These may be separated by three minor marks each, which represent quarter-hours on the clock face, such that if the knob is pointed at the first minor mark clockwise from the topmost major mark, the knob can be said to be in the "12:15" position. Both of these systems are arbitrary values which bear no direct relationship to what the knob actually controls, but they can be used to record and return to a previous position after a knob has been moved. Index marking is particularly important on synths which do not have patch memory; the marks provide a simple way to record values on a patch sheet and recall it later.
Most synths use potentiometers which have smooth round shafts. When the knob is placed on and fastened to the shaft, it needs to be oriented so that when the pot is at its full counterclockwise position, the knob points at the counterclockwise-most index mark. This is known as "indexing" the knob.