Figure 2-9.-Finding total rise and length when unit of run, unitof rise, and total run are known.The twelfths scale may also be used to determinedimensions by inspection for proportional reductions orenlargements. Suppose you have a panel 10 feet 9 incheslong by 7 feet wide. You want to cut a panel 7 feet longwith the same proportions. Set the square, as shown infigure 2-9, but with the blade at 10 9/12 inches and thetongue at 7 inches. Then slide the blade to 7 inches andread the figure indicted on the tongue, which will be4 7/12 inches if done correctly. The smaller panel shouldthen be 4 feet 7 inches wide.Hundredths ScaleThe hundredths scale is on the back of the tongue,in the comer of the square, near the brace table. Thisscale is called the hundredths scale because 1 inch isdivided into 100 parts. The longer lines indicate25 hundredths, whereas the next shorter lines indicate5 hundredths, and so forth. By using dividers, you caneasily obtain a fraction of an inch.The inch is graduated in sixteenths and locatedbelow the hundredths scale. Therefore, the conversionfrom hundredths to sixteenths can be made at a glancewithout the use of dividers. This can be a great helpwhen determining rafter lengths, using the figures of therafter tables where hundredths are given.Figure 2-10.—Using the octagon square.Octagon Scaleeight-The octagon scale (sometimes called thesquare scale) is located in the middle of the face of thetongue. The octagon scale is used to lay out an octagon(eight-sided figure) in a square of given even-inchdimensions.Let’s say you want to cut an 8-inch octagonal piecefor a stair newel. First, square the stock to 8 by 8 inchesand smooth the end section. Then, draw crossed centerlines on the end section, as shown in figure 2-10. Next,set a pair of dividers to the distance from the first to theeighth dot on the octagon scale, and layoff this distanceon either side of the centerline on the four slanting sidesof the octagon. This distance equals one-half the lengthof a side of the octagon.When you use the octagon scale, set one leg of thedividers on the first dot and the other leg on the dotwhose number corresponds to the width in inches of thesquare from which you are cutting the piece.FRAMING SQUARE TABLESThere are three tables on the framing square: the unitlength rafter table, located on the face of the blade; the2-7