Additional pipes, added to the top or bottom of a rank, to permit using the same rank at more than one pitch. For example, the usual 8′ rank has 61 pipes, one for each key on the manual; the largest pipe is 8 feet long, and the pitch sounded on each key is the same as that of the piano (8′, or unison, pitch). A pitch one octave higher than unison (4′ pitch) can be sounded from the same rank by starting with the lowest key of the manual playing the 13th pipe and so on upward; at the top of the rank a 1 2-pipe extension must be added to complete the compass of the manual.