A B C OF THE STEEL SQUARE 



37 



squares are placed against each other and a 

 straight-edge, or against the blade of a third 

 square. If the edges of the squares exactly 

 coincide throughout the squares may be con- 

 sidered correct. 



V* 



Fig. 17. 



Suppose, however, that there is a discrepancy 

 shown by this test, and that as the two squares 

 are placed in the general position, shown in the 

 illustration, they part at the heel, while touch- 

 ing at the ends of the blades, or touching at the 

 heel that they part at the ends of the blades. 



