Stanley Harmonic Analyser model 3 serial 48 in fitted wooden case (one planimeter missing)

The principle of the harmonic analyser was first described by William Thomson (Lord Kelvin) in his Treatise on Natural Philosophy (1879). A few different inventors, like the Germans Olaus Henrici and Otto Mader continued to improve the instrument's design and an increasing number of ready to buy and easy to use models were introduced during the first half of the 20th century. The company Stanley & Co Limited in London constructed harmonic analysers of Mader like design (as per Otto Mader’s model of 1909, also in the Science Museum’s collection) from the 1950s up to 1965. According to the company’s accompanying information pamphlet ''this instrument is designed to carry out the analysis of complex wave forms by the simple action of tracing a curve, which may be of any length within the range of the instrument.''

This model of a series of 3 whose selling price ranged from £200 to £370 was sold with two planimeters and two sets of gears and could calculate up to 18 sine coefficients.