Note 178 — REGISTRATION AND ORNAMENTS OF BACH’S ORGAN WORKS
Wallace Goodrich translation
Oberwerk means literally the higher manual; in two-manual organs the stronger was, at that time, found above the other. The name Rückpositif came from the custom of placing the pipes behind the back (Rücken) of the organist. Finally, the swell bore the name Brustwerk, the pipes being placed facing the breast (Brust) of the player. In a three-manual organ the great keyboard was situated between the swell, which was above, and the choir, which was below it.