A synth circuit, or collection of circuits, whose primary purpose is to generate signals and control voltages used in testing and calibrating other synth equipment, although they may also have musical uses. Standards are most commonly found as modules for modular synthesizers; an example is the Synthesizers.com Q125. This module can generate precise voltage increments; it has two rotary switches, one of which inceases the output voltage by 1V per step, and another which increases the output by 1/12V per step. When this voltage is input to a conventionally scaled Volts/octave VCO, turning the rotary switches will cause the VCO's output frequency to change by one octave or one chromatic half step, respectively. The module also has a stabilized A440 sine wave output to use as a tuning reference.