Caliper is a measuring instrument suitable for measuring (with precision tenths, twentieths, fiftieths and hundredths of a millimetre) the width of an object, the distance between two flat faces in a concavity, the depth of a groove or hole.
A caliper can be a simple compass or be equipped with reading scale, as in the case of the Vernier caliper. The invention of the vernier can be attributed to the Portuguese Pedro Nunes, who published in 1542 a description of an ingenious system to measure small arcs with sufficient accuracy. At the German Ciavius (1640) is attributable the evolution of the vernier and at the French Pierre Vernier (1631, from which is derived the name "Vernier") is attributable the current form of the Vernier caliper. The caliper is used to make measurements with an accuracy of a fraction of a thousandth; it consists in a rod, which on one side is graph, and on the other side is divided in inches and sixteenths of an inch. Furthermore, it presents two jaws for external measurements, two jaws for internal measurements and a tab L for depth measurements.
Caliper is divided in three parts: one fixed, one movable (Vernier) and the little rod.
In the fixed part, there is a jaw upwards and a jaw downwards and the corresponding ones are located in the moving part. The jaws are used to measure the length or the diameter, the small rod is used to measure the depth. The jaws are rounded at the ends, because they are used to measure very small places so that they touch the inside of the circles perfectly.
In calibres more expensive, the small rod is conical in order to measure perfectly even the depths of the cylinders or the cones’ tips (round rod caliper).
On the fixed part, at the bottom there is a scale divided in mm, and at the top there is a scale divided in inches (1 inch=25,4mm). On the movable part (or Vernier), there are two scales, one at the bottom and one at the top. The bottom takes the name of Vernier. The caliper can reach approximations of one-tenth, one-twentieth and one-fiftieth of a millimetre, using the device of Vernier. The vernier is a movable rod, which slides on the fixed rod graduated in millimetres; the length of the vernier scale is divided into “n” equal parts, which correspond to the length of n-1 fixed rod’s parts. Each division of the vernier has a length equal to the ratio (n-1)/n. For example, in the decimal caliper each division of the vernier is equal to (10-1) / 10 = 9/10 of a millimetre.
The most used Vernier calipers are those with twentieth system, whose vernier has a length of nineteen mm with twenty divisions, or fiftieth system, whose vernier measures forty-nine mm and is divided into fifty parties. To avoid reading errors, due to the difficulty of detecting the coincidence of the vernier’s notch with the fixed scale’s notch, there’s a dial caliper whose movable jaws indicates the whole part of the reading, with scanning in multiples of 10 mm, and the pointer indicates the fraction remaining in millimetres and twentieth of a millimetre.
The most easy to use calipers are those with digital liquid crystal display. Digital calipers have a sliding rod usually made of steel and PVC body with electronic card. Generally, the reading of a precision digital caliper is hundredth, but there are pent-thousandth calipers where reading is displayed to 5 thousandths of a millimetre.
Calipers IP67 are often used in places with high quantities of powders and liquids, as they are the almost waterproof. PVC calipers are more fitting when the measurement takes place in the presence of magnetism or with excessive presence of liquids.
Some example of calipers:
• Outside digital caliper;
• Big display digital caliper;
• Digital caliper with metal case;
• High-precision digital caliper with 3V Lithium battery;
• Digital caliper with metal case and protection IP54;
• Digital caliper with metal case and protection IP65;
• Digital caliper with metal case and protection IP67;
• Digital caliper with pent-thousandth resolution;
• Digital depth caliper;
• Digital depth caliper with adjustment extension base;
• Digital caliper with single hook;
• Digital depth caliper with double hook;
• Digital depth caliper with needle;
• Small dimensions digital depth caliper;
• Depth caliper with fine adjustment;
• Depth caliper with single hook;
• Gear tooth Vernier caliper;
• Disk brake Vernier caliper;
• V anvil calipers;
• Inside groove Vernier caliper with flat points;
• Outside groove Vernier caliper with flat points;
• Outside Vernier caliper with fine adjustment;
• Digital caliper without jaws with fine adjustment;
• Extra light alloy digital caliper with “NIPLOY” case;
• Digital caliper aluminium body with jaws in hardened stainless steel;
• Inside groove digital caliper with flat points;
• Outside groove digital caliper with flat points;
• Inside groove digital caliper with round points;
• Outside groove digital caliper with round points;
• Inside groove digital caliper with small jaws;
• Extra-long jaws digital caliper;
• Tube thickness digital caliper;
• Digital caliper with moving measuring jaw;
• Knife-point inside groove digital caliper;
• Arc outside digital caliper;
• Outside digital caliper with fine adjustment;
• Carbon fibre and aluminium digital calipers;
• Single point digital caliper;
• Digital thickness caliper;
• Plane anvil digital caliper;
• Universal groove digital caliper;
• Pointed-jaw digital caliper;
• Inside groove digital caliper with long upper jaws;
• Digital caliper with long upper jaws;
• Inside groove digital caliper with upper jaws;
• Special outside groove digital caliper;
• Special inside groove digital caliper;
• Inside groove digital caliper with round points;
• Knife-point special digital caliper;
• Inside digital caliper for five purposes;
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