THE L3 SYSTEM — QUALITY CONTROL IN MANUFACTURE 975 



SO that large inventories will not accumulate in the factory and delivery 

 commitments can be met. Such a method requires the measurement and 

 classification of the product into groups or cells, followed by the selec- 

 tion of units from such cells in accordance with a required distribution. 

 Although this method requires 100 per cent inspection instead of sam- 

 pling inspection permitted by the use of control charts it was estimated 

 that this method would be used extensively until new manufacturing 

 processes were thoroughly proven and sufficient data collected to fully 

 establish a process capability. 



2.3 THE GENERAL SPECIFICATION 



Anticipated application required consideration and development of 

 methods for the wide variety of manufacturing conditions likely to be 

 encountered in the production of such items as coils, condensers, resistors 

 and vacuum tubes. These products may be manufactured at widely sep- 

 arated factories for assembly in equipment at still another location. In 

 order to assist in the description of the factory applications, to be 

 presented later, the methods developed which are referred to as "dis- 

 tribution requirements" in the general specifications are listed and briefly 

 described below. With the exception of the Records method, distribution 

 requirements are applied to only one characteristic of a product. If ap- 

 plication to more than one characteristic is desirable a method suitable 

 for use as a basis for shipment of the product is selected for the most 

 important characteristic and the Records method is specified for the 

 remaining characteristics. 



1 . Continuous production method. 



2. Batch production method. 



3. Three-cell method. 



4. Records method. 



2.31 Continuous Production Method 



This method is for application where production comprises a reason- 

 ably steady succession of individual units or small groups of units of 

 product from a common source so that individual units as produced may 

 be kept in the order of their production. The criteria of this method apply 

 to a series of units or groups of units of product arranged in the order of 

 their production and are based on the use of control charts for averages 

 and ranges for samples of 5 units each. Examples of typical control charts 

 are shown in Figs. 4 and 5. 



The inclusion of an allowance for the long time variation in the level 



