Why were some keyboards built with more than 50 keys in a single octave?

Keyboards with more than 12 keys per octave were developed to accommodate tuning systems that required distinct pitches for notes that are enharmonically equivalent in modern equal temperament.12

In the meantone temperament system, which was widely used from the 16th to the 18th century, raised keys were often restricted to a single pitch—for example, a key tuned to E♭ could not function as D♯. To overcome this limitation and allow for purer tuning across a wider range of tonalities, makers built instruments with "divided sharps," where the front and back portions of a single key were tuned to different pitches (such as G♯ and A♭).1

Beyond these historical adaptations, more complex keyboards were developed to facilitate microtonal music. By dividing the octave into more than 12 parts, such as 24 equal divisions, musicians could perform intervals like quarter-tones. Some experimental instruments built in the 19th century featured more than 50 keys per octave to permit these highly refined tuning systems.13