686 BELL SYSTEM TECHNICAL JOURNAL 



aspects of the acceptance problem and provides an operationally definite 

 criterion for reducirg inspection for a product whose quality is regularly well 

 controlled within the intent of the specification. 



The procedure developed by the Committee was approved by J.E.T.E.C. 

 (Joint Electron Tube Engineering Council), was approved by the JAN 

 Committee in September 1945, and is reproduced in full in this article. It 

 will be noted that the procedure provides for two Acceptable Quality Levels 

 (AQL), namely 6% defective and 3% defective for individual design test 

 characteristics. Each design test of a particular type of electron tube is 

 classified as either a Standard Design Test with an AQL = 6% or a Special 

 Design Test with an AQL = 3%. For any design test, if product sub- 

 mitted for inspection has quality equal to the AQL, the chances of acceptance 

 are of the order of 94 to 98 out of 100. If quality runs consistently better 

 than the AQL, reduced inspection is permitted, thus serving as an incentive 

 for the manufacturer to strive for better quality. The operatirg characteris- 

 tics of the sampling plans involved are appended to this article and show the 

 degree to which the plans will discriminate for various levels for submitted 

 quality. 



Resonant Circuit Modulator for Broad Band Acoustic Measurements}^ 

 Gordon Ferrie Hull, Jr.* A modulation method is described whereby 

 a broad band frequency response is obtained for recording of sound. In 

 particular low frequency sound approaching zero c.p.s. can be recorded. 

 The theory of the resonant circuit modulating principle is first discussed 

 followed by a description of the apparatus which was constructed for this 

 purpose. 



Quality Reporting — Putting Inspection Results to Work}- Harold R. 

 Kellogg. Quality reportirg is an integral part of the general inspection 

 problem. It cannot be divorced from the logic and aims of an overall inspec- 

 tion program. A discussion of quality reporting should therefore include 

 consideration of (1) inspection procedures, including the collection of data; 

 (2) appraisal of the data; (3) reporting and publicizing results. This out- 

 lines the program as it is discussed in this paper. 



Properties of Monoclinic Crystals}'^ W. P. Mason. Two crystals of the 

 monoclinic s])henoidal class have been found which have modes of vibration 

 with zero temperature coefiicients of frequency, and this jiroperty together 



^^ Jour. Applied Physics, December I'Mft. 



* This research was carried out while the author was a member of the Technical Stall 

 of the lieii Telephone Laboratories, Inc., Murray Hill, New Jersey. 

 '^ Induslrial (Juatity Control, November 1946. 

 '^ Phys. Rev., Nov. 1 and 15, 1946. 



