Square Piano by Schmahl, J

In the center of the key-slip is a lever for lifting the individual dampers; it acts upon the double-armed levers via a rail guided within three diagonal slots. Four additional levers are located on the fixed front panel above the keyboard; from left to right, their functions are: guiding a silk strip between hammer and string; guiding a similar strip of leather (or cloth, according to Kinsky 1910); lifting the damper plate positioned above the strings; and striking the underside of the soundboard with a leather-covered wooden mallet. The keyboard can be shifted 4 mm (the distance between the strings) into the instrument. This causes the hammers to strike the next higher string, thereby transposing the instrument by a semitone. It is locked in the rear position by two metal levers at the front and two metal pins set into the side walls of the keyboard assembly.

Credit: Uni Leipzig