36 A B C OF THE STEEL SQUARE 



right angle, or to use common terms, if the tool 

 is "out of square," that is, if it is in the least 

 inaccurate, its usefulness is destroyed. When 

 the square is inaccurate instead of solving in- 

 tricate geometrical problems correctly it becomes 

 a snare and a delusion, leading to false results 

 and misfits in general. It is somewhat remark- 

 able how few workmen test their squares. I am 

 disposed to believe from long experience that 

 comparatively few mechanics who buy steel 

 squares are cognizant of the possible defects 

 that the tool may have and of the tests which 

 may be applied for the purpose of demonstrat- 

 ing its accuracy. Before proceeding further, 

 therefore, in the discussion of the use of this 

 instrument let us give brief attention to some 

 of the simple methods that may be employed 

 for determining the accuracy of the tool. By 

 way of making practical application of these 

 tests I suggest that at the next dinner hour the 

 reader borrow from his fellow carpenters as 

 many squares as may be convenient, and apply 

 to them more or less of the tests which follow, 

 merely for the purpose of practice, and at the 

 same time to show to what extent the squares in 

 use are correct. 



Fig. 17 shows a very common method of test- 

 ing the exterior angle of a steel square. Two 



