130 BELL SYSTEM TECHNICAL JOURNAL 



The procedure for reading the new volume indicator is essentially 

 the same as that which has always been employed, with the exception 

 that, since the instrument is very nearly critically damped, there need 

 be tolerated fewer overswings above the prescribed deflection. One 

 who is familiar with the use of volume indicators will instinctively read 

 the new instrument correctly. The procedure may be described by 

 stating that the adjustable attenuator, which is a part of the volume 

 indicator, should be so adjusted that the extreme deflections of the 

 instrument needle will just reach a scale reading of zero on the vu scale 

 or 100 on the per cent voltage scale. The volume level is then given 

 by the designations numbered on the attenuator. If, for any reason, 

 the deflections cannot be brought exactly to the vu mark or 100 per 

 cent mark, the reading obtained from the setting of the attenuator may. 

 if desired, be corrected by adding the departure from shown on the 

 vu scale of the instrument. 



Since program material is of a very rapidly varying nature, a reading 

 cannot be obtained instantaneously but the volume indicator must be 

 observed for an appreciable period. It is suggested that a period of 

 one minute be assumed for this purpose for program material, and 5 

 to 10 seconds for message telephone speech, so that the volume level at 

 any particular time is determined by the maximum swings of the 

 pointer within that period. 



Summary of Characteristics 



In the preceding sections of the paper the considerations which led 

 to the selection of the more important characteristics of the new volume 

 indicator have been discussed in some detail. In this section a sum- 

 mary will be made, first of the fundamental requirements which must 

 be conformed to by any instrument if it is to be a standard volume 

 indicator according to the new standards, and secondly, of other re- 

 quirements which have been specified for the new volume indicators 

 which are perhaps matters more of engineering than of a fundamental 

 nature. These requirements are a condensation of the more important 

 features of the specifications for the new insturment. The Weston 

 Electrical Instrument Corporation generously cooperated in the de- 

 velopment, but it is emphasized that the specifications are based on 

 fundamental requirements and are not written on the product of a 

 particular manufacturer. The complete requirements are available 

 to any interested party, and, as a matter of fact, at least one other man- 

 ufacturer has produced an instrument which meets the requirements. 



