The verification of subscribers´ numbers on demand working: A supersonic signal method

To avoid incorrect recording of callers´ numbers in a trunk exchange associated with an automatic area various expedients have been adopted, extending from the reversion of a certain percentage of originating calls to the use of an audible tone. The supersonic method described in this paper was evolved for a country in which the use of a number of languages made the problem more acute. The method is applicable to exchanges already established, and the alterations and additions to equipment are not extensive.