The problems of X-ray crystal structure determination require some type of automatic computing machinery. An evaluation of these problems has lead to the conclusions that a parallel channel relay digital computer operating in conjunction with the standard I. B. M. units will meet the calculation needs of a structure determination and greatly shorten the time and labor involved. A brief description of a relay computer designed to meet these needs has been given. The computer will be able to perform all of the calculations required with the exception of the Patterson and electron density calculations. The latter may be carried out efficiently on standard I. B. M. units.