![Caliper detail view](https://upload.wikimedia.org/wikipedia/commons/1/18/Caliper_detail_view.jpeg)
A caliper (
British spelling
Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the two most notable variations being British and American ...
also calliper, or in
plurale tantum
A ''plurale tantum'' (Latin for "plural only"; ) is a noun that appears only in the plural form and does not have a singular variant for referring to a single object. In a less strict usage of the term, it can also refer to nouns whose singular fo ...
sense a pair of calipers) is a device used to
measure
Measure may refer to:
* Measurement, the assignment of a number to a characteristic of an object or event
Law
* Ballot measure, proposed legislation in the United States
* Church of England Measure, legislation of the Church of England
* Mea ...
the dimensions of an object.
Many types of calipers permit reading out a measurement on a ruled scale, a dial, or a digital display. Some calipers can be as simple as a
compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
with inward or outward-facing points, but no scale. The tips of the caliper are adjusted to fit across the points to be measured and the dimension read by measuring between the tips with another measuring tool, such as a
ruler
A ruler, sometimes called a rule, line gauge, or scale, is a device used in geometry and technical drawing, as well as the engineering and construction industries, to measure distances or draw straight lines.
Variants
Rulers have long ...
.
It is used in many fields such as
mechanical engineering
Mechanical engineering is the study of physical machines that may involve force and movement. It is an engineering branch that combines engineering physics and mathematics principles with materials science, to design, analyze, manufacture, and ...
,
metalworking
Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale ...
,
forestry
Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forests, woodlands, and associated resources for human and environmental benefits. Forestry is practiced in plantations and natural stands. Th ...
,
woodworking
Woodworking is the skill of making items from wood, and includes cabinet making (cabinetry and furniture), wood carving, woodworking joints, joinery, carpentry, and woodturning.
History
Along with Rock (geology), stone, clay and animal parts, ...
,
science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence for ...
and
medicine
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...
.
Plural vs. singular
A single tool might be referred to as a "caliper" or as "calipers", like a pair of scissors or glasses (a "plural only" or ''
plurale tantum
A ''plurale tantum'' (Latin for "plural only"; ) is a noun that appears only in the plural form and does not have a singular variant for referring to a single object. In a less strict usage of the term, it can also refer to nouns whose singular fo ...
'' form). In colloquial usage, the phrase "pair of verniers" or just "
vernier" might refer to a vernier caliper. Colloquially these phrases can also refer to dial calipers, although they involve no vernier scale.
In machine-shop usage, the term "caliper" is often used in contradistinction to "
micrometer Micrometer can mean:
* Micrometer (device), used for accurate measurements by means of a calibrated screw
* American spelling of micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
", even though outside micrometers are technically a form of caliper. In this usage, "caliper" implies only the
form factor of the vernier or dial caliper (or its digital counterpart).
History
The earliest caliper has been found in the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
Giglio wreck near the
Italian
Italian(s) may refer to:
* Anything of, from, or related to the people of Italy over the centuries
** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom
** Italian language, a Romance language
*** Regional Ita ...
coast. The ship's find dates to the 6th century BC. The wooden piece already featured a fixed and a movable jaw.
[Roger B. Ulrich: ''Roman woodworking'', Yale University Press, New Haven, Conn., 2007, , p.52f.] Although rare finds, calipers remained in use by the Greeks and
Romans
Roman or Romans most often refers to:
*Rome, the capital city of Italy
* Ancient Rome, Roman civilization from 8th century BC to 5th century AD
*Roman people, the people of ancient Rome
*''Epistle to the Romans'', shortened to ''Romans'', a lette ...
.
A bronze caliper, dating from 9 AD, was used for minute measurements during the Chinese
Xin dynasty
The Xin dynasty (; ), also known as Xin Mang () in Chinese historiography, was a short-lived Chinese imperial dynasty which lasted from 9 to 23 AD, established by the Han dynasty consort kin Wang Mang, who usurped the throne of the Emperor Ping o ...
. The caliper had an inscription stating that it was "made on the ''gui-you'' day, the first day of the first month of the first year of ''Shijianguo'' ." The calipers included a "slot and pin" and "graduated in inches and tenths of an inch."
[. An abridged version.]
![东汉铜卡尺](https://upload.wikimedia.org/wikipedia/commons/3/34/%E4%B8%9C%E6%B1%89%E9%93%9C%E5%8D%A1%E5%B0%BA.jpg)
The modern vernier caliper was invented by
Pierre Vernier
Pierre Vernier (19 August 1580 at Ornans, Franche-Comté (at that time ruled by the Spanish Habsburgs, now part of France) – 14 September 1637, same location) was a French mathematician and instrument-inventor. He was the inventor and epony ...
, as an improvement of the
nonius of
Pedro Nunes.
Types
Inside calliper
![InsideCalipers](https://upload.wikimedia.org/wikipedia/commons/c/c3/InsideCalipers.jpg)
The inside callipers are used to measure the internal size of an object.
* The upper caliper in the image (on the right) requires manual adjustment prior to fitting. Fine setting of this caliper type is performed by tapping the caliper legs lightly on a handy surface until they will ''almost'' pass over the object. A light push against the resistance of the central pivot screw then spreads the legs to the correct dimension and provides the required, consistent ''feel'' that ensures a repeatable measurement.
* The lower caliper in the image has an adjusting screw that permits it to be carefully adjusted without removal of the tool from the workpiece.
Outside caliper
![OutsideCalipers](https://upload.wikimedia.org/wikipedia/commons/7/71/OutsideCalipers.jpg)
Outside callipers are used to measure the external size of an object.
The same observations and technique apply to this type of caliper, as for the inside caliper. With some understanding of their limitations and usage, these instruments can provide a high degree of accuracy and repeatability. They are especially useful when measuring over very large distances; consider if the calipers are used to measure a large diameter pipe. A vernier caliper does not have the depth capacity to straddle this large diameter and at the same time reach the outermost points of the pipe's diameter. They are made from high carbon steel.
Divider caliper
![DividerCalipers](https://upload.wikimedia.org/wikipedia/commons/c/cd/DividerCalipers.jpg)
In the metalworking field, a divider caliper, popularly called a compass, is used to
mark out locations. The points are sharpened so that they act as scribers; one leg can then be placed in the dimple created by a
center or prick punch and the other leg pivoted so that it scribes a line on the workpiece's surface, thus forming an arc or circle.
A divider caliper is also used to measure a distance between two points on a map. The two caliper ends are brought to the two points whose distance is being measured. The caliper's opening is then either measured on a separate ruler and then converted to the actual distance, or measured directly on a
scale drawn on the map. On a
nautical chart
A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land (topographic map), natural features of the seabed, details of the coa ...
the distance is often measured on the
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
scale appearing on the sides of the map: one
minute of arc
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
along any
great circle
In mathematics, a great circle or orthodrome is the circular intersection of a sphere and a plane passing through the sphere's center point.
Any arc of a great circle is a geodesic of the sphere, so that great circles in spherical geomet ...
, e.g. any longitude meridian, is approximately one
nautical mile
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as the meridian arc length corresponding to one minute ( of a degree) of latitude. Today ...
or 1852
meter
The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its prefi ...
s.
Dividers are also used in the medical profession. An ECG (also EKG) caliper transfers distance on an
electrocardiogram; in conjunction with the appropriate scale, the heart rate can be determined. A pocket caliper version was invented by cardiologist Robert A. Mackin.
Oddleg caliper
![OddlegCalipers](https://upload.wikimedia.org/wikipedia/commons/8/83/OddlegCalipers.jpg)
Oddleg calipers, Hermaphrodite calipers, or Oddleg Jennys, as pictured on the left, are generally used to scribe a line at a set distance from the edge of a workpiece. The bent leg is used to run along the workpiece edge while the scriber makes its mark at a predetermined distance, this ensures a line parallel to the edge.
In the diagram at left, the uppermost caliper has a slight shoulder in the bent leg allowing it to sit on the edge more securely. The lower caliper lacks this feature but has a renewable scriber that can be adjusted for wear, as well as being replaced when excessively worn.
Vernier caliper
![Vernier caliper](https://upload.wikimedia.org/wikipedia/commons/f/f6/Vernier_caliper.svg)
The labelled parts are
The callipers in the diagram show a primary reading on the metric scale of about 2.475 cm (2.4 cm read from the main scale plus about 0.075 cm from the vernier scale).
Calipers often have a "zero point error": meaning that the callipers do not read 0.000 cm when the jaws are closed. The zero point error must always be subtracted from the primary reading. Let us assume these callipers have a zero-point error of 0.013 cm. This would give us a length reading of 2.462 cm.
For any measurement, reporting the error on the measurement is also important. Ignoring the possibility of interpolation by eye, both the primary reading and the zero point reading are bounded by plus/minus ''half'' the length corresponding to the width of the smallest interval on the vernier scale (0.0025 cm). These are "absolute" errors and absolute errors add, so the length reading is then bounded by
plus/minus the length corresponding to the ''full'' width of the smallest interval on the vernier scale (0.005 cm). Assuming no systematics affect the measurement (the instrument works perfectly), a complete measurement would then read 2.462 cm ± 0.005 cm.
The vernier, dial, and digital callipers directly read the distance measured with high
accuracy and precision
Accuracy and precision are two measures of ''observational error''.
''Accuracy'' is how close a given set of measurements ( observations or readings) are to their ''true value'', while ''precision'' is how close the measurements are to each oth ...
. They are functionally identical, with different ways of reading the result. These callipers comprise a calibrated scale with a fixed jaw, and another jaw, with a pointer, that slides along the scale. The distance between the jaws is then read in different ways for the three types.
The simplest method is to read the position of the pointer directly on the scale. When the pointer is between two markings, the user can mentally
interpolate
In the mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points.
In engineering and science, one often has a n ...
to improve the precision of the reading. This would be a simply calibrated calliper, but the addition of a
vernier scale
A vernier scale, named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, thereby increasing resolution and reducing measurement unc ...
allows more accurate interpolation and is the universal practice; this is the vernier calliper.
Vernier, dial, and digital callipers can measure internal dimensions (using the uppermost jaws in the picture at right), external dimensions using the pictured lower jaws, and in many cases depth 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
metric
Metric or metrical may refer to:
* Metric system, an internationally adopted decimal system of measurement
* An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement
Mathematics
In mathem ...
measurements on the lower part of the scale and
inch
Measuring tape with inches
The inch (symbol: in or ″) is a unit of length in the British imperial and the United States customary systems of measurement. It is equal to yard or of a foot. Derived from the Roman uncia ("twelfth") ...
measurements on the upper, or vice versa, in countries that use inches. Vernier calipers commonly used in industry provide a precision to 0.01 mm (10
micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
s), or one thousandth of an inch. They are available in sizes that can measure up to 1828 mm (72 in).
Dial caliper
![TESA CCMA-P 150 mm 0](https://upload.wikimedia.org/wikipedia/commons/8/89/TESA_CCMA-P_150_mm_0.02_mm_dial_caliper.jpg)
Instead of using a vernier mechanism, which requires some practice to use, the dial caliper reads the final fraction of a millimeter or inch on a simple dial.
In this instrument, a small, precise
rack and pinion
A rack and pinion is a type of linear actuator that comprises a circular gear (the '' pinion'') engaging a linear gear (the ''rack''). Together, they convert rotational motion into linear motion. Rotating the pinion causes the rack to be driven ...
drives a pointer on a circular
dial, allowing direct reading without the need to read a vernier scale. Typically, the pointer rotates once every inch, tenth of an inch, or 1 millimeter. This measurement must be added to the coarse whole inches or centimeters read from the slide. 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 the size of subsequent objects relative to the master object).
The slide of a dial caliper can usually be locked at a setting using a small
lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or ''fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is div ...
or screw; this allows simple
go/no-go
A go/no go test is a two-step verification process that uses two boundary conditions, or a binary classification. The test is passed only when the ''go'' condition has been met and also the ''no go'' condition has been failed.
The test gives no in ...
checks of part sizes.
Digital caliper
![2020 Suwmiarka cyfrowa](https://upload.wikimedia.org/wikipedia/commons/5/5c/2020_Suwmiarka_cyfrowa.jpg)
A popular refinement replaces the analog dial with an electronic display that shows the reading as a numeric value. Rather than a
rack and pinion
A rack and pinion is a type of linear actuator that comprises a circular gear (the '' pinion'') engaging a linear gear (the ''rack''). Together, they convert rotational motion into linear motion. Rotating the pinion causes the rack to be driven ...
, these calipers use a
linear encoder
A linear encoder is a sensor, transducer or readhead paired with a scale that encodes position. The sensor reads the scale in order to convert the encoded position into an analog or digital signal, which can then be decoded into position by a di ...
. Most digital calipers can be switched between centimeters or millimeters, and inches. All provide for zeroing the display at any point along the slide, allowing the same sort of differential measurements as with the dial caliper. Digital calipers may contain a "reading hold" feature, allowing the reading of dimensions after use in awkward locations where the display cannot be seen.
Ordinary 6-inch (150 mm) digital calipers are made of stainless steel, have a rated accuracy of 0.001 in (0.02 mm) and a resolution of 0.0005 in (0.01 mm).
The same technology is used to make longer 8-inch and 12-inch calipers; the accuracy for longer measurements declines to 0.001 in (0.03 mm) for 100–200 mm and 0.0015 in (0.04 mm) for 200–300 mm.
Increasingly, digital calipers offer a serial data output to allow them to be interfaced with a dedicated recorder or a
personal computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...
. The digital interface significantly decreases the time to make and record a series of measurements, and it also improves the reliability of the records. A suitable device to convert the serial data output to common computer interfaces such as
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
,
Universal Serial Bus
Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...
, or wireless can be built or purchased. With such a converter, measurements can be directly entered into a
spreadsheet
A spreadsheet is a computer application for computation, organization, analysis and storage of data in tabular form. Spreadsheets were developed as computerized analogs of paper accounting worksheets. The program operates on data entered in cel ...
, a
statistical process control
Statistical process control (SPC) or statistical quality control (SQC) is the application of statistical methods to monitor and control the quality of a production process. This helps to ensure that the process operates efficiently, producing m ...
program, or similar software.
The serial digital output varies among manufacturers. Common options are
*Mitutoyo's Digimatic interface. This is the dominant name brand interface. Format is 52 bits arranged as 13 nibbles.
*Sylvac interface. This is the common protocol for inexpensive, non-name brand, calipers. Format is 24 bit 90 kHz synchronous.
*Starrett
*Brown & Sharpe
*Federal
*Tesa
*Aldi. Format is 7 BCD digits.
*Mahr (Digimatic, RS232C, Wireless FM Radio, Infrared and USB)
Like dial calipers, the slide of a digital caliper can usually be locked using a lever or thumb-screw.
Some digital calipers contain a
capacitive linear encoder. A pattern of bars is etched directly on the
printed circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
in the slider. Under the scale of the caliper another printed circuit board also contains an etched pattern of lines. The combination of these printed circuit boards forms two variable
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s. The two capacitances are out of phase. As the slider moves the capacitance changes in a linear fashion and in a repeating pattern. The circuitry built into the slider counts the bars as the slider moves and does a linear interpolation based on the magnitudes of the capacitors to find the precise position of the slider. Other digital calipers contain an inductive linear encoder, which allows robust performance in the presence of contamination such as coolants. Magnetic linear encoders are used in yet other digital calipers.
Micrometer caliper
A caliper using a calibrated
screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
for measurement, rather than a slide, is called an ''external micrometer caliper gauge'', a ''micrometer caliper'' or, more often, simply a ''micrometer''. (Sometimes the term ''caliper'', referring to any other type in this article, is held in contradistinction to ''micrometer''.)
Comparison
Each of the above types of calipers has its relative merits and faults.
Vernier calipers are rugged and have long-lasting accuracy, are coolant proof, are not affected by magnetic fields, and are largely shockproof. They may have both centimeter and inch scales. However, vernier calipers require good eyesight or a
magnifying glass
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle. A magnifying glass can be used to focus light, such as to concentrate the sun's radiation to crea ...
to read and can be difficult to read from a distance or from awkward angles. It is relatively easy to misread the last digit. In production environments, reading vernier calipers all day long is error-prone and is annoying to the workers.
Dial calipers are comparatively easy to read, especially when seeking the exact center by rocking and observing the needle movement. They can be set to 0 at any point for comparisons. They are usually fairly susceptible to shock damage. They are also very prone to getting dirt in the gears, which can cause accuracy problems.
Digital calipers switch easily between centimeter and inch systems. They can be set to zero easily at any point with a full count in either direction and can take measurements even if the display is completely hidden, either by using a "hold" key, or by zeroing the display and closing the jaws, showing the correct measurement, but negative. They can be mechanically and electronically fragile. Most also require batteries and do not resist coolant well. They are also only moderately shockproof and can be vulnerable to dirt.
Calipers may read to a resolution of 0.01 mm or 0.0005 in, but accuracy may not be better than about ±0.02 mm or 0.001 in for 150 mm (6 in) calipers, and worse for longer ones.
Use
![Measuring saltmarsh sparrow (50237104216)](https://upload.wikimedia.org/wikipedia/commons/c/cc/Measuring_saltmarsh_sparrow_%2850237104216%29.jpg)
A caliper must be properly applied against the part in order to take the desired measurement. For example, when measuring the thickness of a plate a vernier caliper must be held at right angles to the piece. Some practice may be needed to measure round or irregular objects correctly.
Accuracy of measurement when using a caliper is highly dependent on the skill of the operator. Regardless of type, a caliper's jaws must be forced into contact with the part being measured. As both part and caliper are always to some extent
elastic
Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics.
Elastic may also refer to:
Alternative name
* Rubber band, ring-shaped band of rubber used to hold objects togeth ...
, the amount of force used affects the indication. A consistent, firm touch is correct. Too much force results in an under indication as part and tool distort; too little force gives insufficient contact and an over indication. This is a greater problem with a caliper incorporating a wheel, which lends
mechanical advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The device trades off input forces against movement to obtain a desired amplification in the output force. The model for t ...
. This is especially the case with digital calipers, calipers out of adjustment, or calipers with a poor quality beam.
Simple calipers are uncalibrated; the measurement taken must be compared against a scale. Whether the scale is part of the caliper or not, all analog calipers—verniers and dials—require good eyesight in order to achieve the highest precision. Digital calipers have an advantage in this area.
Calibrated calipers may be mishandled, leading to loss of
zero
0 (zero) is a number representing an empty quantity. In place-value notation
Positional notation (or place-value notation, or positional numeral system) usually denotes the extension to any base of the Hindu–Arabic numeral system (or ...
. When a calipers' jaws are fully closed, it should, of course, indicate zero. If it does not, it must be recalibrated or repaired. A vernier caliper does not easily lose its calibration but a sharp impact or accidental damage to the measuring surface in the caliper jaw can be significant enough to displace zero.
Digital calipers have zero set buttons, for quick recalibration.
Vernier, dial and digital calipers can be used with accessories that extend their usefulness. Examples are a base that extends their usefulness as a depth gauge and a jaw attachment that allows measuring the center distance between holes. Since the 1970s a clever modification of the moveable jaw on the back side of any caliper allows for step or depth measurements in addition to external caliper measurements, in similar fashion to a universal micrometer (e.g., Starrett Mul-T-Anvil or Mitutoyo Uni-Mike).
Zero error
![Vernier scale zero error +0](https://upload.wikimedia.org/wikipedia/commons/2/21/Vernier_scale_zero_error_%2B0.10.gif)
The method to use a vernier scale or caliper with zero error is to use the formula "actual reading = main scale + vernier scale − (zero error)". Zero error may arise due to knocks that affect the calibration at 0.00 mm when the jaws are perfectly closed or just touching each other. Positive zero error refers to the fact that when the jaws of the vernier caliper are just closed, the reading is a positive reading away from the actual reading of 0.00 mm. If the reading is 0.10 mm, the zero error is referred to as +0.10 mm. Negative zero error refers to the fact that when the jaws of the vernier caliper are just closed, the reading is a negative reading away from the actual reading of 0.00 mm. If the reading is −0.08 mm, the zero error is referred to as −0.08 mm.
See also
*
Cruising rod A cruising rod is a simple device used to quickly estimate the number of pieces of lumber yielded by a given piece of timber. Similarly to a yardstick, it is a rod with markings. The estimation is carried out as follows. Standing at arm's length fr ...
*
Dial indicator
*
Lens clock
A lens clock is a mechanical dial indicator that is used to measure the dioptric power of a lens. It is a specialized version of a spherometer. A lens clock measures the curvature of a surface, but gives the result as an optical power in diopters ...
*
Pace stick
A pace stick is a long stick usually carried by warrant officer and non-commissioned officer drill instructors in the British and Commonwealth armed forces as a symbol of authority and as an aid to military drill.
A pace stick usually consists of ...
Notes
References
External links
RS-232 Interface Design Details For Digital Caliper
{{Authority control
Ancient Greek technology
Chinese inventions
Greek inventions
Length, distance, or range measuring devices
Metalworking measuring instruments
Woodworking measuring instruments