A METHOD OF RATING MANUFACTURED PRODUCT 351 



inspection. For convenience, the rate is made a relative figure which 

 incorporates the features of index numbers used by the economist. 

 Just as the index numbers of cost of Hving, wages, corn production, 

 etc., indicate current conditions relative to some reference condition as 



T J ivT I, -I r>n Current Cost of Living 



Index Number = 100 ._,, . „ r r ■ ■ -, 



1914 Cost of Livmg 



so does the rate reflect current quality relative to that of a selected 

 standard of reference. One of the features of the rate is its assistance 

 in controlling quality, its provision of means for discriminating between 

 chance and non-chance variations from the quality level which should 

 currently be expected. 



Character of Inspection 



As in other fields much of the inspection work on telephone products 

 consists of critical examinations of essential features to determine 

 whether or not the units of product conform with specification require- 

 ments. This is done: 



(1) By visual examinations in which ob\ious defects of material or 



workmanship are discovered by eye. 



(2) By using "Go" and "No Go" gauges or their equivalent, which 



determine whether a unit does or does not conform with a re- 

 quirement, or 



(3) By using measuring instruments which reveal the numerical mag- 



nitude of the characteristic for each unit tested. 



To illustrate the last two kinds of inspection, the specification 

 requirement for the capacity of a type of condenser is "not less than 

 .099 microfarad and not more than .101 microfarad." Inspection may 

 be done by the "Method of Attributes," using a test set which shows 

 merely whether the capacity of a condenser is inside or outside of the 

 limits, or by the "Method of Variables," using an indicating or re- 

 cording meter to show the numerical value of capacity for each test. 

 In these two cases the data, if tabulated, would appear as in Fig. 1. 

 Inspection data used for rating come in both varieties. 



Items which Enter the Rate 



Commercial measurement of quality by inspection usually consists 

 in a comparison with stated requirements. Starting with the design 

 and a knowledge of what can be accomplished in the shop, allowances 

 for variations in materials, dimensions and salient properties are 

 established in specifications. The aggregate of specification require- 

 ments constitutes a standard of quality which the manufacturer holds 



