12 ABC OF THE STEEL SQUARE 



or ground until they are straight and true. The 

 outside edge of the blade should also be 

 "trued" up and made exactly parallel with the 

 inside edge, if such is required. The same proc- 

 ess should be gone through on the tongue. As 

 a rule, squares imade by firms of repute are per- 

 fect, and require no adjusting; nevertheless, it 

 is well to make a critical examination before 

 purchasing. 



The next thing to l>e considered is the use of 

 the figures, lines, and scales, as exhibited on 

 the square. It is supposed that the ordinary 

 divisions and sub-divisions of the inch, into 

 halves, quarters, eighths, and sixteenths are 

 understood by the student ; and that he also 

 understands how to use that part of the square 

 that is subdivided into twelfths of an inch. 

 This being conceded, we now proceed to de- 

 scribe the various rules as shown on all good 

 squares ; but before proceeding further, it may 

 not be out of place to state, that on the squares 

 recommended in this book, one edge is sub- 

 divided into thirty-seconds of an inch. 



This fine sub-division will be found very use- 

 ful, particularly so when used as a scale to 

 measure drawings made in half, one-quarter, one- 

 eighth or one-sixteenth of an inch to the foot. 



