Sonometer, Three Wire Pattern

A hollow wooden sounding box with scales divided in mm between fixed bridges over which three wires are stretched. To one wire, spring balance reading to 100 x5 N is fitted and the tension exerted and measured can be finely adjusted by a wing-nut. Another wire passes over a pulley and can be loaded as desired. A third wire is provided for comparison, its tension may be adjusted by means of a wrest-pin
The distance between the fixed bridges is 72 cm. Complete with three movable bridges, wrest-pin key and a set of steel wires, length 1.5 m of 22, 24, and 26 SWG.
The pack of replacement wires, sold separately, has steel and brass wires, each in 22, 24, and 26 SWG.
Dimensions (L x W x H): 129 x 13 x 11 cm.