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BELL SYSTEM TECHNICAL JOURNAL 



unmistakably on the drawing his analysis of the required functioning of the 

 part and the manner in which he intends the tolerances to apply, in the 

 event that there is any possibility of misunderstanding. 



The essence of this problem and some of the possibilities of solution can 

 best be seen by reference to drawings which illustrate the major points. 



Figure 5 shows the drawing of a flat plate dimensioned from center lines 

 but without any tolerances whatever. Some minor dimensions not in- 

 volved in this discussion are omitted in the interest of simplification but 

 the part shown is in every way a normal one. The meaning of the drawing 

 is completely clear and can be interpreted in but one way no matter from 



5.250" 



Fig. 5 — Flat plate dimensioned without tolerances 



what standpoint the analysis is made. The reason for this is obviously 

 that but one value is shown for every dimension. 



Figure 6 shows this same drawing dimensioned in exactly the same way 

 with the exception that tolerances are shown for most of the dimensions. 

 To the uninitiated it might appear to present no more problem than the 

 previous drawing without tolerances because of the tendency to visualize 

 the drawing in terms of the nominal dimensions only. 



When the engineer analyzes the effect of the combinations of the various 

 tolerances shown, interesting questions immediately arise. In the first 

 place the combination of holes dimensioned 1.25"' ± .002" from the center 

 line appears to be definitely located because on the drawing the center 

 line is shown in a definite position. Yet when the tolerances are considered 



