Complex sentence: Historically, the palettes were manipulated by a ratchet swell, a lever operated by the foot to the side of the console that will fit into two or three different notches that lock the position of the lever, and therefore the shutters, in place.
Split into simpler sentences: Historically, the palettes were manipulated by a ratchet swell, a lever operated by the foot to the side of the console. The lever would fit into two or three different notches, which would lock the position of the lever, and therefore the shutters, in place.