Fuente: Wipo "digitalization" 762,284. Digital encoders and decoders. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Dec. 24, 1954 [Jan. 7, 1954], No. 456/54. Class 40 (1). A digital encoder comprises means for representing a magnitude, e.g. a displacement or rotation, in a cyclic permuting binary-decimal code in which the digits 0 to 9 of a cyclic permuting decimal code are represented in a binary code which is cyclic permuting at least for the representation of the digits 0 to 9 and from 9 directly to 0. A digital decoder is provided with means for converting a cyclic permuting binary-decimal code into normal decimal form. The digits of the cyclic permuting decimal code are obtained from a normal decimal number by substituting for a digit in the decimal number the complement on nine of the digit whenever the immediately preceding digit of greater significance in the decimal number is odd, e.g. the decimal number 497,649 is represented by 492,349 in the cyclic permuting decimal code. Similarly 497,650 is represented by 492,359, and whereas in changing from 492,349 to 492,359 only one digit is altered, and that by unity, in changing from one to the other corresponding number in the normal decimal system two digits are altered. A normal decimal number is obtained from digits in the corresponding cyclic permuting decimal code by substituting for a digit in the code the complement on nine of that digit when and only when the decoded, normal, decimal digit of next greater order of significance is odd, and a method of determining this is to sum all the uncoded cyclic permuting decimal digits of greater significance than that of the digit to be converted and if this sum is odd, the digit should be complemented on nine, and if even should be left unchanged. The cyclic permuting binary code is preferably such that an odd number of digits 1 in a binary word represents an odd cyclic permuting decimal digit, and is such that not only does not more than one binary digit change for each unit change between 0 and 9, but also not more than one binary digit changes during the change from 9 directly to 0. For ease in decoding it is arranged that the binary words representing N and (9-N) differ by only one binary digit, i.e. the complementing digit, e.g. 0101 = 0, 1101 = 9, 0001 = 1, 1001 = 8, and so on. Encoder. A copper disc, Fig. 1, is notionally divided into one hundred sectors, conducting portions being shown as cross-hatched and the remaining portions representing depressions which are filled with insulating material. The disc is divided notionally into eight annular rings Y1 to Y8 which co-operate with brushes (not shown) and define binary digits 1 or 0 according to whether there is a conducting portion or depression at a given point. The outer rings Y1 to Y4 define by means of a cyclic permuting binary code the less significant digit of a cyclic permuting decimal word,'which itself defines one of the hundred sectors. The inner rings Y5 to Y8 define the more significant digit. With the preferred code, one ring in each group of four may be dispensed with by placing two brushes staggered relative to one another on one of the rings. Alternatively the disc may be made from transparent material with opaque portions corresponding to the conducting portions on the copper disc, the code being obtained as pulse train by means of a beam of light which scans the disc radially and cooperates with a photo-electric cell. Two or more discs may be geared together by Geneva stop mechanism. Decoder. A decoder operating in the parallel mode, Fig. 2, comprises a converter 20 for converting signals in the binary-decimal cyclic permuting code into signals representing in a cyclic permuting binary code the digits of the corresponding normal decimal number, and converters 21, 22, 23, for converting the binary digits representing the normal decimal number into normal decimal form. The rule for effecting this conversion is that the digits of the cyclic permuting binary code representing a cyclic