You can get a direct reading of a caliper setting if you use the ordinary calipers. At the same time, you must measure a caliper setting with a rule. However, you can use slide calipers to cope with this disadvantage. This instrument is also called a caliper rule.Slide calipers can be used for measuring outside, inside, and other dimensions. One side of the caliper is used as a measuring rule, while the scale on the opposite side is used in measuring outside and inside dimensions. Graduations on both scales are in inches and fractions thereof. A locking screw is incorporated to hold the slide caliper jaws in position during use. Stamped on the frame are two reading the scale while making inside and outside measurements, repectively.To measure the outside diameter of round stock, or the thickness of flat stock, move the jaws of the caliper into firm contact with the surface of the stock. Read the measurement at the reference line stamped OUT.When measuring the side diameter of a hole, or the distance between two surface, insert only the rounded tips of the caliper jaws into the hole or between the two surfaces. Read the measurement on the reference line stamped IN.If the caliper is used to measure both outside and inside dimensions two reference lines are needed, and that they are separated by an amount equal to the outside dimension of the rounded tips when the caliper is closed.In general, pocket models of slide calipers are made in 3-in. and 5-in. sizes and are graduated to read in 32nds and 64ths. Pocket slide calipers are available when extreme precision is not required. They are frequently used for duplicating work when the expense of fixed gages is not warranted.