Control knob

A control knob is a rotary control used to provide input to a device when grasped by an operator and turned, so that the degree of rotation corresponds to the desired input. Such knobs are one of the most common components in control systems and are found on all sorts of devices.

Overview

Such knobs vary greatly in form, but as a rule they are expected to be grasped by the fingertips. By convention a clockwise rotation ordinarily produces an "increased" input, whatever that is understood to be. Knobs may turn continuously or may have detents to produce discrete selections; they commonly have a scale with a pointer to aid achievement of the desired setting, though it is common for the gradations in the scale to have no concrete meaning (e.g. the markings of a volume control). There is frequently a fixed "off" position at the origin of movement in which the knob actuates a switch shutting down whatever behavior is controlled, rather than having a separate on/off switch.

Operation