ABC OF THE STEEL SQUARE 



This evidently shows that one of the squares is 

 inaccurate, or possibly that both are inaccurate. 

 How is the inaccuracy to be located? The two 

 squares may be placed face to face, with the 

 blades upward from an even surface, say the 

 face of the third square or the jointed ed^e of 



a board, and so 

 held that their 

 heels, for exam- 

 ple, shall coin- 

 cide. Then glance at the edges of 

 the blades. If they exactly coincide 

 it would indicate that the error is 

 evenly divided between the two 

 squares, a very improbable occur- 

 rence. Compare the two squares in 

 the reverse position, that is, with the 

 tongues extending upward. Then 

 apply the test shown in Fig. 18, and 

 finally that shown in Fig. 19. 



By trying the squares one inside 

 of the other, as shown in Fig. 18, 

 the exterior angle is compared with 

 the interior angle. If the edges 

 throughout fit together tightly, first using one 

 square inside and then the other, it is almost con- 

 clusive evidence that both the squares are accu- 

 rate. 



! 



Fig. 18. 



