Bias is a term denoting a lengthening or shortening of transmitted teletypewriter signal impulses by the electrical characteristics of the transmitter. When these characteristics lengthen each signal, it is said to have marking or positive bias. When these characteristics reduce the length of each signal, it is said to have spacing or negative bias. Bias can largely compensated for in the receiving apparatus by changing the spring tension of the relay. Thus, if a line has marking bias, the spring tension of the relay can be increased so its contacts close a little later and open a little earlier for each signal, and the length of time the relay contacts are closed can usually be made the same as the length of time of a perfect signal.
See also: I-97