A hollow wooden sounding box, 1290 x 130 x 110 mm (l x w x h) provided with scales divided in mm, between fixed bridges over which the wires are stretched. To one wire a spring balance reading to 100 N x 5 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. The distance between the fixed bridges is 720 mm. Complete with three moveable bridges, wrest-pin key.
OPTIONAL
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