The concept of true intonation keyboards traces back to the 16th Century, with the work of Italian musicologists Gioseffo Zarlino and Nicola Vicentino.

Around 1850, American inventor Henry Ward Poole created an enharmonic organ, which did not require finger substitution upon note changes.

[2] The German physicist Hermann von Helmholtz also experimented on this theme during this period, using his own instrument - the Reinharmonium.

[3] German physicist Arthur von Oettingen became interested in microtonal tuning in the 1870s, later developing the idea for a harmonium using 72 or 53 keys, with which almost any chord using thirds, fourths, and fifths.

Unlike a piano, where there are only twelve keys per octave, on an Orthotonophonium, the player has the choice of several pitches per tone.