ITU-T R.53-1989 Permissible Limits for the Degree of Distortion on an International 50-Baud/120-Hz VFT Channel (Frequency and Amplitude Modulation) - Telegraph Transmission (Study Group IX) 2 pp
that to test the effective margin of the receiver of a start-stop teleprinter it is desirable to standardize the content of the transmitted sequence of signals
ITU-T R.53-1989 history
1989ITU-T R.53-1989 Permissible Limits for the Degree of Distortion on an International 50-Baud/120-Hz VFT Channel (Frequency and Amplitude Modulation) - Telegraph Transmission (Study Group IX) 2 pp