MONOCHORD (Gr. µovb op6ov, rcavwv µovvucos)  : med . Lat. monochordum), an instrument having a single string, used by the ancient Greeks for tuning purposes and for measuring the scale arithmetically . The monochord, as it travelled westwards during the middle ages, consisted of a long board, or narrow rectangular box, over which was stretched the single string; along the edge of the sound-board was drawn a line divided according to simple mathematical ratios to show all the intervals of the scale . A movable bridge was so contrived as to slide along over the string and stop it at will at any of the points marked . The vibrating length of string, being thus determined as on the guitar, lute, violin, &c., yielded a note of absolutely correct pitch on being twanged by fingers or plectrum . In order the better to seize the relation of various intervals, a second string tuned to the same note, but out of reach of the bridge, was sometimes added to give the fundamental . (K .