Apparatus for determining the standard deviation mechanically

The calculating apparatus here described is a natural development from the “harp” harmonic analyser and similarly makes use of loaded strings, which apply forces to a flexible yoke, whose consequent movement resolves these forces automatically. The use of vertical strings in place of the horizontal ones employed in the “harp” being convenient for the special purpose of this apparatus, it became possible so to design it as to give quantitative amplitudes to the yoke movements, which in the “harp” were only qualitative.Purpose of Employment . The purpose of the apparatus is to enable tolerably precise calculations of standard deviation and other related statistical constants to be made quickly, and in the hands of persons other than trained computers. Much of the work done in any laboratory is necessarily restricted by considerations of time and labour to the production of figures which in any one set of observations are not sufficiently numerous to justify laborious statistical treatment. Or, equally, the known imperfections of material or of method may themselves result in errors in the computed statistical constant, so that computation of,e. g ., a standard deviation beyond two significant figures would have no real value. In both cases an approximate determination is all that the circumstances warrant, and only then if that determination can be made rapidly by anybody available. The present apparatus makes this possible.