558 BELL SYSTEM TECHNICAL JOURNAL 



way the effects on articulation of various kinds of physical performance 

 of a telephone circuit can be investigated. 



The master reference system itself will be used chiefly for the im- 

 portant work of rating working standard systems and instruments. 

 These working standards can be simpler than the master system and 

 can be provided in any number required to handle the rating of 

 commercial circuits and apparatus. 



The working standard may be of several forms. It can be similar 

 to the master reference system, simplified in its detailed construction 

 but capable of calibration by the means employed for calibrating the 

 master reference system. Such a system would probably find employ- 

 ment in laboratories and factories where the volume of testing is 

 sufficient to justify the use of such apparatus. Another form may 

 include electrostatic or electrodynamic instruments which are not 

 capable of being measured by the calibration equipment of the master 

 reference system. A third form which the working standard may 

 take is that involving the use of transmitters, receivers and station 

 sets such as have been used in the standard cable reference system. 

 These latter types of working standards can be calibrated by volume 

 comparisons with the master system or with the first type of working 

 standard. They will find their chief field of usefulness at such points 

 as shops for the repair and recovery of station apparatus, where the 

 volume of work is not sufficient to justify the expense involved in 

 maintaining more elaborate working standards. 



European Master Reference System 



In Europe the recommendation of technical standards for telephony 

 is a function of the Comite Consultatif International des Communi- 

 cations Telephoniques a Grande Distance (C.C.I.), which is composed 

 of representatives of the various European telephone administrations. 

 In 1926, at the invitation of the C.C.I., representatives of the Bell 

 System met in London with a committee appointed by the C.C.I, to 

 consider the adoption of a transmission reference system. This com- 

 mittee recommended that the C.C.I, adopt as their master reference 

 system a system essentially the same as the one described in this 

 paper, and that such a system, which would be a replica of one in 

 New York, be installed in Paris in the laboratory of the C.C.I, and 

 be known as the European Master Reference System. This recom- 

 mendation was adopted by the C.C.I. 



Subsequently, some improvements were made in the system, and 

 two duplicate systems, each with its associated calibrating apparatus, 

 have been constructed. One of these is now in the Bell Telephone 



