Combination pistons (general and divisional), reversibles, and often MIDI couplers and other miscellaneous controls appear in the form of thumb pistons.
As the name implies, thumb pistons are designed to be pressed by the thumb that can reach down from the manual that is being played (see example). However, a piston located above a manual that is being played can be pressed by one of the other fingers (see example).
You may wish to review the introduction to Thumb Piston Locations in the lesson, “Introduction to the Organ Console.”
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