Recommendation U.2
STANDARDIZATION OF DIALS AND DIAL PULSE GENERATORS
FOR THE INTERNATIONAL TELEX SERVICE
(former CCIT Recommendation E.2, 1951;
amended at Arnhem, 1953 and Geneva, 1956)
	The CCITT,
considering
	(a)	that, when dials and dial pulse generators are used for the process of automatic selection by subscribers to the international telex network, it is advantageous to standardize as far as possible the characteristics of such dials and dial pulse generators;
	(b)	that the standardization of the dialling speed and lost motion periods of dials presents no technical difficulty;
	(c)	that, for the satisfactory working of certain automatic systems, the time between successive pulse trains should not be less than 500 milliseconds, but that experience has shown that the minimum time taken by an experienced operator to rotate the dial is of the order of 300 milliseconds;
	(d)	that pulse ratios from 1.2:1 to 1.9:1 will ensure the satisfactory working of existing automatic switching systems;
	(e)	that these pulse ratios can be usefully adopted with a view to simplifying direct calling between subscribers,
unanimously declares the view
	(1)	that in the international telex service, when dials or dial pulse generators are used for the automatic selection of subscribers:
a)	the dialling speed shall be standardized at 10 pulses per second with a tolerance of ± 10%;
b)	the lost motion period of dials shall be not less than 200 milliseconds nominal value;
c)	the inter–digit pause of dial pulse trains generated by dial pulse generators shall not be less than 600 milliseconds;
(2)	a)	that the pulse ratio must be between 1.2:1 and 1.9:1, the nominal ratio may be chosen as lying between 1.5:1 or 1.6:1;
b)	that when the selection signals pass through a regenerative repeater it may be advantageous to use a nominal ratio of 1.5:1.