There have been variations in the design of the keyboard to address technical and musical issues. The earliest designs of keyboards were based heavily on the notes used in Gregorian chant (the seven diatonic notes plus B-flat) and as such would often include B♭ and B♮ both as diatonic "white notes," with the B♮ at the leftmost side of the keyboard and the B♭ at the rightmost. Thus, an octave would have eight "white keys" and only four "black keys. " The emphasis on these eight notes would continue for a few centuries after the "seven and five" system was adopted, in the form of the short octave: the eight aforementioned notes were arranged at the leftmost side of the keyboard, compressed in the keys between E and C (at the time, accidentals that low were very uncommon and thus not needed). During the sixteenth century, when instruments were often tuned in meantone temperament, some harpsichords were constructed with the G♯ and E♭ keys split into two. One portion of the G♯ key operated a string tuned to G♯ and the other operated a string tuned to A♭, similarly one portion of the E♭ key operated a string tuned to E♭, the other portion operating a string tuned to D♯. This type of keyboard layout, known as the enharmonic keyboard, extended the flexibility of the harpsichord, enabling composers to write keyboard music calling for harmonies containing the so-called wolf fifth (G-sharp to E-flat), but without producing aural discomfort in the listeners (see: Split sharp). The "broken octave," a variation of the aforementioned short octave, similarly used split keys to add accidentals left out of the short octave. Other examples of variations in keyboard design include the Jankó keyboard and the chromatic keyboard systems on the chromatic button accordion and bandoneón.