A caliper is a device used to measure the distance between two symmetrically opposing sides. Calipers typically use a precise slide movement for inside, outside, depth or step measurements. WESTport is an authorized distributor of Dial, Electronic (Digital), Vernier and Specialty Calipers. Some caliper types are used for comparing or transferring dimensions.
A Dial Caliper has a small gear rack that drives a pointer on a circular dial. Typically, the pointer rotates once every inch, tenth of an inch, or 1 millimeter, allowing for a direct reading without the need to read a vernier scale (although one still needs to add the basic inches or tens of millimeters value read from the slide of the caliper). The dial is usually arranged to be rotatable beneath the pointer, allowing for "differential" measurements (the measuring of the difference in size between two objects, or the setting of the dial using a master object and subsequently being able to read directly the plus-or-minus variance in size of subsequent objects relative to the master object).
The slide of a dial caliper can be locked at a setting using a small lever or screw; this allows simple go/no-go checks of part sizes.
Digital (Electronic) Caliper
A refinement in calipers is the replacement of the analog dial with an electronic digital display on which the reading is displayed. Some digital calipers can be switched between metric and inch units. All provide for zeroing the display at any point along the slide, allowing the same sort of differential measurements as with the dial caliper but without the need to read numbers that may be upside down. Digital calipers may contain some sort of "reading hold" feature, allowing the reading of dimensions even in awkward locations where the display cannot be seen.
Even with all of these benefits, digital calipers have by no means replaced the dial caliper. Digital calipers typically do not have the beam structure of a dial or vernier caliper and therefore do not have the repeatability or accuracy to an amateur user.
Digital calipers offer a serial data output. Measurements can be taken and instantly stored in a spreadsheet or similar piece of software, significantly decreasing the time taken to take and record a series of measurements. Like dial calipers, the slide of a digital caliper can usually be locked using a lever or thumb-screw. Both dial and digital calipers can be used with accessories that extend their usefulness.
A variation to the more traditional caliper is the inclusion of a vernier scale; this makes it possible to directly obtain a more precise measurement.
Vernier calipers can measure internal dimensions, external dimensions using the lower jaws and depending on the manufacturer, depth measurements by the use of a probe that is attached to the movable head and slides along the centre of the body. This probe is slender and can get into deep grooves that may prove difficult for other measuring tools. The vernier scales may include both metric and inch measurements on the upper and lower part of the scale.
Vernier calipers commonly used in industry provide a precision to a hundredth of a millimeter (10 micrometers) or one thousandth of an inch. A more precise instrument used for the same purpose is the micrometer.