ABC OF THE STEEL SQUARE 



39 



By tests of the kinds just described among 

 several squares, the mechanic will soon perceive 

 from the several ascertained results that one or 

 the other of the several squares that he is hand- 

 ling is more accurate than all the others, if not 

 absolutely accurate. There still remains the 



Fig. 19. 



need of a test, however, to prove the absolute 

 accuracy of the particular square which he be- 

 lieves to be about right. On a drafting table, 

 r a smooth board, let him next perform the fol- 

 lowing experiment, which is one of the several 

 that might be mentioned in this connection; 



