Where p = Process average fraction defective 



n = Average number of articles in first samples inspected 



during the summary period. * 



For example, the records for a typical period of 10 weeks might show 



the following: 



Total number of articles inspected in first samples = 16,400 



Process average fraction defective = p = .00557 or .56% 



^, 16,400 ,^,^ 



Ihus, n = — — - = 1640 articles 

 10 



Hence : 



Upper Control Limit = .00557 + 2 



/ 



005 57 (1 - .005 57) 

 1640 



'' = .00557 + .00368 

 " = .00925 = .93% 

 Lower Control Limit = .00557 - .00368 

 " = .00189 = .19% 



2. Application of the Double Sampling Plan by the Inspector 

 The following flow chart illustrates in sequence the basic steps involved 

 in the inspection of a lot. 



Inspect First Sample 



^ i 



If the Number of Defectives 

 found in the First Sample 



Does not exceed 

 the AN of the First 

 Sample 



i 



Exceeds the AN of the First 

 Sample but does not exceed the 

 AN of the First and Second 

 Samples combined 



i 



Inspect Second Sample 



i 



If the Number of Defectives 

 found in the First and Second 

 Samples Combined 



i 

 Exceeds the AN of 

 the First and Second 

 Samples combined 



Does not exceed the 

 x-\N of the First and 

 Second Samples 

 Combined 



i 

 Exceeds the AN of 



the First and Second 

 Samples Combined 



Pass the Lot 



Detail or Reject the Lot 



46 



