An important difference between larger and smaller organ consoles is the number of manuals they contain.
Two manuals are standard for smaller instruments--the Great and the Swell. The Great is the lower and the Swell is the upper manual.
On a three-manual organ the new manual is added below the Great. This Choir or Positiv manual becomes the first manual, the Great becomes the second manual, and the Swell the top, or third manual.
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Two-Manual Organ Consoles