ABC OF THE STEEL SQUARE 43 



creased in size. If the size of the drafting table 

 permits, therefore, extend the line drawn along 

 the tongue of the square to 2 feet. Extend that 

 drawn along the blade to 4 feet. In doing this 

 care must be taken that the lines thus extended 

 are fair to the tool under examination, for if 

 they are not drawn in a way to strictly coincide 

 with the edges of the square then the test is of no 

 avail. Then measure from the ends of these 

 lines, that is, from a point 3 feet from the heel 

 up the tongue to a point 4 feet from the heel 

 along the blade. If this diagonal distance is 

 exactly 5 feet it will show that the angle repre- 

 sented by the heel of the square, as I have de- 

 scribed it, is a right angle, #nd that, therefore, 

 the test is accurate. 



Now let us next examine a little more care- 

 fully the relationship of the square to fre- 

 quently required lines. It is a common thing 

 among carpenters to use 12 of the blade and 

 12 of the tongue for a right angle or squaru 

 miter. Why are these figures employed, or to 

 put the question otherwise, how is it determined 

 that 12 and) 12 are the proper figures? Per- 

 haps the question can be made still clearer by 

 another illustration. It is common to s?iy that 

 12 of the blade and 5 of the tongue is correct 

 for the octagon miter. How is this determined? 



