An electromechanical device is described for computing the two‐dimensional structure factor formulas,r=1Nfrsincos2&pgr;hursincos2&pgr;kvr  and  r=1Nfrsincos2&pgr;(hur+kvr).fr, ur, vrare fractional and may be fed in to the third decimal place;handkmay vary from −20 to +20. Each term in the series is computed individually to an accuracy of approximately ½&percent; and is automatically added to the existing sum whilst the next term is being computed. The speed of computation is generally equal to the speed with which the variables of each term are fed into the computer. The machine makes use of ``magslip'' resolvers for computation of the trigonometrical functions.