A binary encoding scheme in which a signal parameter, such as electric current or voltage, undergoes a change in a significant condition or level every time that a "zero" occurs, but when a "one" occurs, it remains the same, i.e., no transition occurs. Note 1: The transitions could also occur only when "ones" occur and not when "zeros" occur. If the significant condition transition occurs on each "one," the encoding scheme is called "non-return to zero mark" (NRZ-M. ) Note 2: NRZ-S and NRZ-M signals are technically interchangeable; i.e., one is the logical "NOT" (inverse) of the other. It is necessary for the receiver to have prior knowledge of which scheme is being used. Without such knowledge, it is impossible for the receiver to interpret the data stream correctly; i.e., its output may be the correct data stream or the logical inverse of the correct data stream. Synonym non-return-to-zero.