In data communications, the ratio of (a) the time to transmit a text automatically at a specified modulation rate to (b) the time actually required to receive the same text at a specified maximum error rate. Note 1: All of the communication facilities are assumed to be in the normal condition of adjustment and operation. Note 2: Telegraph communications may have different temporal efficiency factors for the two directions of transmission. Note 3: The practical conditions of measurement should be specified, especially the duration of the measurement.