Assertion: electric organ's keyboard | /r/HasProperty | a treadle-style potentiometer
Facets:
value: for controlling the volume
type: PURPOSE
Source sentences:
text: A few of the bass pedals designed to be used with electronic or clonewheel organs have features that operate the upper manual keyboards, such as a expression pedal or swell pedal, which is a treadle-style potentiometer for controlling the volume; buttons to turn on or change the speed of a Leslie speaker, a rotating horn speaker in a cabinet; or program change buttons, which send a MIDI message to the other upper keyboards to change to a new sound or setting.