Changing fashions in the number of manuals

At one time, one octave was divided into a 14 note scale, with different pitches for D♯ and E♭, and for G♯ and A♭. For a time, manuals had seven individual white keys with five individual black keys above, and then two keys known as "split keys" perched above that. The organist would choose whether to play D♯ or E♭, or G♯ or A♭, at the time of the performance, in accordance with tonality.