A METHOD OF RATING MANUFACTURED PRODUCT 355 



(1) 



fli W2 



Demerits per unit 

 for all types of defects, where 



Wi, Wi, etc. = weight (demerits per defect) for defects of type 1, 2, 



etc. 

 di, di, etc. = number of type 1, 2, etc., defects, and 

 Wi, W2, etc. = number of units inspected for type 1,2, etc., defects. 



Instead of using equation (1) directly for indicating quality, it has 

 seemed desirable to establish a rate which by its numerical magnitude 

 gives an immediate indication of whether the quality is better or worse 



♦10 



Better Than Base Period Quality 

 -•s— Base Period Rate «= 



Poorer Than Base Period Quality^ 



J F M A IC J 

 Month 



Poorer Than Base Period Quality 



'^— Base Period Index » 1 



Better Than Base Period Quality 



J F M A M J 

 Month 

 Fig. 3 — Relation between index and rate for a given product and period of time 



than that of some easily recognized reference condition. Resorting to 

 methods commonly used in constructing index numbers, we therefore 

 select a base period during which the manufacturing conditions and 

 inspection methods were known to be essentially the same as at the 

 present time, determine the demerits per unit for the representative 

 data of that period, and set up the following index: 



Index = 



Current Demerits per Unit 

 Base Period Demerits per Unit 



(2) 



