has to be provided. This is commonly done by having a threaded wire end on the wooden tracker rods. A circular nut varies the effective length of the tracker where it engages with other parts of the action. One objective of correct regulation is that the keys on each manual have the same rest height and distance of travel when pressed. The regulation wrongly set at one extreme can cause a note to sound when no keys are pressed. This may also be caused by the action sticking after the key is released. The other extreme is that notes do not sound, or sound feebly, when a key is pressed. Kinds of action Besides tracker action, two other kinds of action used in pipe organs are as follows: Electric action in which electric valves are used to allow wind into the pipes Pneumatic action in which compressed air is used to control valves that allow wind into the pipes Advantages and disadvantages of tracker action Currently, some organ builders use tracker action in new organs, others use electric action, and still others use either type depending on the instrument. There are builders and organists who have strong feelings regarding the advantages of one type of action over another. Advantages Tracker action gives the organist more precise control over the exact moment air enters the pipe. This control affects the attack and release of a note through different touch. Before the invention of electric action, the organ was a touch-sensitive instrument. Tracker action requires less maintenance than other types of action since there are no pneumatics to be re-leathered, no electric contacts to tarnish and no wires to break. Disadvantages The console or keydesk (where the organist actually plays) cannot be moved. On some instruments, as more stops are used, the organist must apply more pressure/force to a key in order for it to play, resulting in heavy playing action when playing full organ. This can be particularly burdensome when two or more manuals are coupled. Problems of heavy action can almost always be overcome through correct use of body weight. The invention of the Barker lever was also meant to counteract this problem, by providing a pneumatic assist while retaining a completely-mechanical action. Remote placement of sections of the organ are dependent on the distance the mechanical linkages can successfully extend, as opposed to the unlimited extendability of electric wires