magnitude and a negative sign these discoveries made possible the use of read only memory rom 60 of dimension 24 u00d7 5 rom 60 functions as a look up table such that for a given combination of input signals rom 60 is able to determine which of the 24 possible magnitudes should be selected sign designator 62 performs the function of determining whether each of the 24 possible magnitudes generated by rom 60 has a positive polarity or a negative polarity sign designator 62 determines the proper polarity of the rom output signal generally by sensing the polarity of the mp signal which is available at output conductor 68 of multiplexer 16 sign designator 62 must also determine if the one exception to this general polarity relationship is present the polarity of the mp signal is determinative of the polarity of the rom output signal except during bt1 a plurality of output conductors 76 from timing generator 22 transmit a timing signal corresponding to bt1 through bt6 to sign designator 62 when sign designator 62 senses te bt1 time interval it then compares the m1 mp s1 and sp input signals which are transmitted to it via conductors 66 68 70 and 72 if sign designator 62 determines that during bt1 there is an m1 magnitude with a positive polarity and an s2 magnitude with a negative polarity it will then generate a sign signal opposite that of the mp polarity.