18U 



DLLL SYSTEM TECHNICAL JOURNAL 



ance of ± .010". When greater accuracy is required three-place decimals 

 are used to express a minimum and a maximum value. 



The adoption of decimal dimensioning for all drawings prepared at BeU 

 Telephone Laboratories is being actively considered. However, adoption 



TABLE I 



History or United States Dimensional Standards 



Year 



1830-36 



1856 

 1866 



1893 



1933 



1937-41 



Action 



Resulting Dimensional Relationships 



Adoption for Customs Service and for distribution to individual states of 

 standards intended to be the English yard based on a certain portion of 

 an 82 inch bar imported in 1813. The portion selected was supposed 

 to be identical with the English yard. 



Official copy of new British Imperial 

 Yard accepted as standard 



Congress declared metric units law- 

 ful and established legal equiva- 

 lents 



Mendenhall Order set up Inter- 

 national meter as the fundamental 

 standard 



American Standards Association 

 (Representing Industry) adopts 

 1 inch = 2.54 centimeters 



Bill before Congress but held in 

 committee for amendments 



International Meter 



= 39.370147 

 British Inch 



Legal Meter 

 U. S. 



in = 39.37 



British Inch 



International Meter = 39.37 



U. S. Inch 



International Meter = 39.370078 

 U. S. Inch 



International Meter = 39.370078 

 U. S. Inch 



TABLE II 

 Examples of Ford Decimals Compared to Common Fractions 



of decimal dimensioning would not of itself result in any changes in our 

 system for establishing tolerance values. 



Raw Material Sizes 



In contrast to this continued trend toward simplification and rationaliza- 

 tion of our systems of dimensional units raw material supply is still com- 

 plicated by a multitude of obsolete systems of gauge sizes in every day use. 



