Generally, calipers are used in biology to take measurements. There are several kinds of calipers based on the principle of a pair of arms or jaws. One jaw is fixed and the other is movable, which are designed to measure the distance between two points.(Measuring instruments with two movable arms, known to biologists as dividers, are also called calipers in the dictionary.) Dial calipers have been the most widely used. They are easy to handle and read ; although, to avoid errors, the user must be aware that the indicator needle of some brands makes a complete revolution in 5 mm, others in 10mm. They look like the electronic digital calipers but with a dial instead of digital display. Obsolete and less easy to read, but still found in some laboratories, vernier calipers require that measurements be interpreted from a sliding scale. Digital calipers show the measurement through an LCD(liquid crystal display) are replacing dial and vernier calipers. These calipers are more accurate and easier to read than their predecessors. Electronic versions can be interfaced with a computer so that measurements can be entered directly into a database file .Giant calipers, known as anthropometers , are used other objects up to dimensions of 2 meters.
Some dial calipers have adjustable needle-tipped jaws designed for point-to-point measurements. Most calipers, designed for measuring nuts ,bolts and mechanical parts, come with blunt jaws unsuited for measuring fragile objects such as tiny skulls and bones. The jaws of these calipers must be ground down to finer tips. Grinding should be done by a professional who will avoid overheating the metal. This is especially important for electronic calipers.
Whenever a part of an object is measured, two points must be touched by the jaws of the calipers. These two points define the measurement. The reference point is the point of the pair that can be most accurately and securely touched by the fixed jaw of the calipers. With the fixed jaw on the reference point, the movable jaw is closed down carefully until it touches the other point. Each measurement is repeated until there is a consistent result.