Figs. 2 and 3 show this effect exaggerated. _B_ is the block against which the scale abuts. The dotted line indicates where the caliper leg should rest, but cannot do so, unless the scale is held perfectly square with the block. Fig. 4 shows a method of setting the calipers by using a small square to abut the scale and to afford a surface against which to place the leg of the caliper. The scale, lying flat on the blade of the square, is always sure to be square edgewise, and is easily held squarely against the stock of the square as shown. This method has also the advantage of being portable, and can be taken to the window or to any place where the light is satisfactory. When using a long scale, the free end may be held against the body to assist in holding it in place.[2] Shoulder Calipers [Illustration: Fig. 5. Shoulder Calipers] In Fig. 5 are shown a pair of calipers which are very handy in measuring work from shoulder to shoulder or from a shoulder to the end of the piece of work. For this purpose they are much handier, and more accurate, than the ordinary "hermaphrodites." The legs are bent at _AA_ so as to lie flat and thus bring the point of the long leg directly behind the short one which "nests" into it, as at _B_, so that the calipers may be used for short measurements as well as for long ones. Double-jointed Calipers to Fold in Tool Box In Fig. 6 are illustrated a pair of large calipers that can be folded up and put in a machinist's ordinary size tool chest. The usual large caliper supplied by the average machine shop is so cumbersome and heavy that this one was designed to fill its place. It can be carried in the chest when the usual style of large caliper cannot. It is a very light and compact tool. It is a 26-inch caliper, and will caliper up to 34 inches diameter. The top sections are made in four pieces, and the point ends fit between the top half like the blade of a knife, as shown in the engraving. Each side of the upper or top section is made of saw steel 1/16 inch thick, and the lower part or point of steel 1/8 inch thick. The double section makes the tool very stiff and light. The point section has a tongue _A_, extending between the double section, which is engaged by a sliding stud and thumb nut. The stud is a nice sliding fit in the slot, and the thumb nut clamps it firmly in place when in use. _B_, in the figure, shows the construction of the thumb nut. _C_ is a sheet copper liner put between the washers at _A_. The dotted lines in the engraving show the points folded back to close up. The large joint washers are 1¾ inch diameter, and a 5/8-inch pin with a 3/8-inch hexagon head screw tightens it up. The forward joints are the same style, but smaller. The main joint has two 1¾-inch brass distance pieces or washers between the two main washers. The top section is 12½ inches between centers, and the point sections 15 inches from center to point. Closed up, the calipers measure 16 inches over-all.