Paired disparity code

In telecommunication, a paired disparity code is a code in which some or all of the characters are represented by two sets of digits of opposite disparity[?] that are used in sequence so as to minimize the total disparity of a longer sequence of digits.

Note 1: An alternate mark inversion signal[?] is an implementation of a paired disparity code.

Note 2: The digits may be represented by disparate physical quantities, such as two different frequencies, phases, voltage levels, magnetic polarities, or electrical polarities, each one of the pair representing a 0 or a 1.

Source: from Federal Standard 1037C and from MIL-STD-188