170 



can be used for all ordinary purposes, when not required for those 

 for which it is especially designed, and is applicable to the measure- 

 ment of extended dimensions by a simple reduction in the value of the 

 proportional parts. For which reason the graduations are in inches 

 and twelfths of an inch, to represent with greater ease the measure- 

 ment of feet and inches in its practical application. 



Upon examination of the above diagram, it will be observed that 

 the letter A designates the ordinary carpenter's square, and the letter 

 B the moveable limb, which is connected with it by steel pins and a 

 securing thumb-screw, C These pins are arranged so as to traverse 

 with ease in the slots which appear in the diagram, in both members 

 of the square, and also in the moveable limb, thus allowing the limb 

 to take any position that may be required in either or both members 

 of the square, and securing it in such a position by the thumb-screw, 

 C. The dotted line, shown in the diagram, on the principal member 

 of the square, represents the position of the moveable limb when not 

 required for use. In this position it does not interfere with the use of 

 the square for ordinary purposes, the width of the limb being such 

 as not to conceal the graduations of the square. It is to be observed, 

 that the length of the limb is such that, when placed at the extreme 

 of the slots heretofore described, the ends of the graduated edge will 

 correspond with the ends of the graduated edges of each member of 

 the square, and any deviation therefrom will show, at a glance, when 

 the instrument is out of square. 



The practical mechanic will at once discover the value of this in- 

 strument in many instances in his daily labours, combining, as it 

 does, accuracy, simplicity and rapidity of operation, and securing 

 economy of time and material. For instance, in its application to 

 braces, in ordinary framing, where the footing and bearing being 

 known, the length and mitre of each end can be determined in a mo- 

 ment. So, also, in the construction of carriagts for stairs, the rise 



