Book 4 - Operation of the Organ Controls Exploring USER and Library Access Stops. Here we study the controls of the organ that affect registrations. We fully examine organ stops and their use. As a reminder there are two large groups of stops on these organs, in addition to the stops whose names appear on the stop tablets or knobs, stops that are immediately available at all times to the organist. Voice Palette(TM) stops are assigned to stop tablets...