An accurate voice-frequency-level calibrating set for field use

In order to maintain the accuracy of loss measurements commensurate with the requirements of direct distance dialing (DDD), very accurate test tones are needed. This paper describes a rugged, portable calibrating set used to insure the accuracy of the test tones. A telephone craftsman may use this set to adjust the level of a signal with 0.3% accuracy. A means for analytically determining the accuracy of such a set is given in the Appendix.