412 BELL SYSTEM TECIIXICAL JOURNAL 



been calibrated in 800-c\clc miles, and as the TU is of the same 

 nature as this unit, no ditilirulties are encountered in arranging the 

 sets to read directly in TU. 



New sets will be manufactured on this basis, but ii will, of course, 

 be desirable in order to avoid frequent con\-ersion of data from one 

 unit to the other, to arrange many of the sets which are already in 

 use in the plant to read in TU. It is not planned to convert the sets 

 which depend upon ear comparisons, such as the- 1-A and 1-B trans- 

 mission measuring sets and the recei\er shunts used in some cases 

 for checking up repeater gains, as tiie tlifference wlien measuring 

 small values is not great and these sets arc generalh' used for a class 

 of work where the required precision is not sufficient to warrant their 

 conversion to the new basis. Visual reading sets, however, such as 

 2-A, 3-A and 4-A transmission measuring sets and the 2-A repealer 

 gain set, give results which are accurate to about 0.1 TU and are 

 usually used for work where a fairly high degree of precision is re- 

 quired. These sets can be changed to read directly in TU at a com- 

 paratively small expense as it is only necessary to change the cali- 

 bration of the measuring dials and slide wire potentiometers and the 

 values of certain of the resistances associated with them. The cost 

 of making these changes will be reduccKJ by the fact that it is i^lamied 

 to make certain other desirable changes which will effect inipro\e- 

 nii'iits in the operation of the sets at the same time. Complete loss 

 data in terms of TV wiiirji are nece.ssary for checking measured 

 eiiiiix alents, have liccn ])rci)arcd and will replace the data formerly 

 iisi'd. 



In toil line inaiiitcn.iiirc wmk. record cards are kept which show 

 tin- l,i\i)Ut of till! ciriiiits and liic transmission losses of the com- 

 ponent parts of each circuit together with the total loss which should 

 be obtained by test if the circuit is not in trouble. In changing o\er 

 from miles to TV these record cards will lie re\ ised to show losses 

 in the ni'W iniit. 



("KOSSr.M.K ("oMI't r.\tI(INS 



In h.indliiig certain t\pes of crosstalk pri)l)lcms, it has beiMi Idiiiid 

 con\enient to express crosstalk in terms of transmission units rather 

 than crosstalk units. Miles of stantlard cable have previously 

 been used in such problems. 77' can be used for this purpose as well 

 as miles and it is somewh.ii sim])lir to make the conversion from 



'Sec a paper liy I'. II. Best, "Measuring MetluKls for MainlainitiK the Trans- 

 mission Kfficiency of Telephone Circuits." Joiirn. A.LE.E ., Vol. XI. Ill, 1924. 





