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BELL SYSTEM TECHNICAL JOURNAL 

 TABLE I 



Comparison of the Economic Factors on Testing of Protector Blocks by 

 Machine Method and by Manual Method 



Note: This means that a master gage or parts that are .0001 in. outside the 

 lolerance limit will be rejected, in the first case, an average of 95 times in 100 trials, 

 and in the second case 45 times. Parts that are .0001 in. within the tolerance limits 

 will be passed as good in the same ratios. The disposition of parts that vary more 

 than .0001 in. either way from the tolerance limits would follow the normal probability 

 law. The figures given do not give any indication of the very small percentage of 

 defective parts that would be passed as good or good parts classed as defectives, as 

 these would depend upon the relative number of defectives and the distribution of 

 their variations from the tolerance limit, as well as the precision of the methods given 

 above. 



The development of machine gaging has been greatly aided by the 

 development of accessory parts, such as reliable indicating gages, 

 chromium-plated parts, sensitive but sturdy relays, vacuum tube 

 amplifiers and photo-electric cells. 



