Abstract: The invention relates to an acoustic piano having a fretbase on which at least one fret node is supported by a fret and an adjacent node spaced from the fret node. Selected piano strings press downwardly upon the nodes and define between the nodes a duplex scale portion of the piano strings. A plate is located beneath the fretbase and is pressed downwardly by the fretbase due to pressure of the strings. The invention provides a method of moving the fretbase portion relative to the plate in a direction parallel to the piano strings. The method includes the steps of providing a force-applying tool including a mandrel portion, and a force-transmitting head having a force-transmitting surface and a surface for sliding on the plate. The tool is oriented so that a main axis of the mandrel portion angles downwardly towards a plane of the piano strings, with the force-transmitting surface abutting a force-receiving surface of the fretbase, and with the sliding surface abutting the plate.