The CCITT,considering(a) that the duration of the transmitting start-stop cycle of terminal start-stop apparatus should be at least 7.4 units for apparatus operating at 50 and 75 bauds,7.5 units for apparatus operating at 100 bauds;(b) that the effective net margin should be greater than:?35% for signals sent by a transmitter having a nominal cycle equal to or greater than 7 units (for operation at 50 or 75 bauds),?30% for signals sent by a transmitter having a nominal cycle equal to or greater than 7.2 units (for operation at 100 bauds).
ITU-T R.60-1988 Referenced Document
ITU-T R.140 Definitions of Essential Technical Terms in the Field of Telegraph Transmission - Telegraph Transmission (Study Group IX) 32 pp*， 1989-01-01 Update
ITU-T R.60-1988 history
1988ITU-T R.60-1988 CONDITIONS TO BE FULFILLED BY REGENERATIVE REPEATERS FOR START-STOP SIGNALS OF INTERNATIONAL TELEGRAPH ALPHABET No. 2