Calipers are the oldest types of comparison measuring tools, and they are also the so-called “skill tools”. The calipers depend on “feel” to measure a part, then transfer the dimension to a precision rule, micrometer or slide caliper, and get a good reading.To achieve this goal the user must master some skills and experiences. If used properly, the calipers can measure to at least .004″or 0.01mm It requires as light a touch as possible to measure with a caliper for most comparisions are made with rules, where the caliper is laid against the screw adjustment, while the firm-joint is held by friction.Spring-type and firm-joint are the two general designs of calipers and dividers. Spring-type calipers are tensioned against the screw adjustment, while the firm-joint is held by friction.Caliper sizes refer to the distance from the fulcrum to the end of the leg. The measuring capability of spring-type calipers and dividers is approximately the same as the size. The measuring capability of firm-joint and lock-joint calipers is approximately one-third more than the size.Caliper points are not hardened because they only compare measurements. The contact points can be easily shaped in whatever manner desired. All divider points are quite hardened.Usually, dividers and trammels are set to rule graduations and can be set more accurately than calipers.