Petherick code
The Petherick code is a one-step code, like the Gray code or the Glixon code. The Petherick code differs from the codes mentioned in that it does not use the two code words 0000 and 1111, the same applies to the Gray-Excess code and the O'Brien code.
The code words of the Petherick code are constructed in such a way that the 9's complement is obtained by inverting the most significant bit( MSB). The mathematical complement facilitates the representation and calculation with negative numbers and the subtraction of numbers.
The Petherick code is used in control engineering, for example in angle encoders.