Vernier caliper

How it works

The jaws are closed on the work and the slide is locked. The beam carries the main scale. The slide carries the vernier plate, whose divisions are slightly shorter than the beam’s divisions: on Starrett’s 25-division vernier the beam is divided in twenty-fifths of an inch (0.025 inch) and the vernier plate has 25 parts of 0.001 inch each. The user reads the beam at the zero line of the vernier, then finds the one vernier line that coincides with a beam line and adds its value.

Starrett’s bulletin gives the method as a count of inches, tenths and twenty-fifths on the beam plus the number of vernier graduations to the coinciding line, each worth 0.001 inch.

Anatomy

Beam: The graduated bar carrying the fixed jaw; Starrett’s caliper beam is graduated on both sides, for outside and inside measurements.
Fixed jaw: The jaw at the end of the beam. Brown & Sharpe’s 1904 catalog describes the jaws of its calipers as hardened and ground.
Sliding jaw and vernier plate: The slide carrying the second jaw and the vernier scale.
Clamp screw and fine adjusting nut: The clamp locks the slide; the adjusting nut then brings the jaws to the work by a small amount. Starrett’s procedure is to close the jaws by hand, lock the clamp, turn the fine adjusting nut, and lock the vernier clamp before taking the caliper off the work.
Divider centers: Center points on the beam and slide so that dividers and trammel points can be set to the measured distance.

Variants

Early sliding calipers with vernier: Instruments of the early nineteenth century such as the Science Museum Group’s triangular-pattern Holtzapffel vernier external callipers of 1800–1825 and the workshop vernier caliper of about 1830.
Pocket vernier caliper: A short vernier caliper; Brown & Sharpe’s 1904 catalog discusses its 6-inch and 12-inch vernier calipers and a pocket pattern.
Vernier depth gage: The vernier slide stays fixed and forms a base, and the graduated blade moves to find the depth (Starrett bulletin).
Vernier height gage: A caliper turned into a standing gage with a scriber on the slide, used on a surface plate to mark vertical distances.
Gear tooth vernier caliper: Combines a depth and a caliper slide to measure the chordal thickness of a gear tooth; Starrett and Brown & Sharpe both list one.
Dial caliper and digital caliper: Mitutoyo’s history dates the dial caliper to 1960 (Mauser, Helios) and the first incremental digital calipers to 1977 (TESA; a capacitance type by Ingvar Andermo commercialized by C. E. Johansson).

Specifications

Vernier resolution, inch · in: 0.001Starrett’s 25-division and 50-division verniers each read 0.001 inch.
Vernier resolution, metric · mm: 0.02Starrett’s 25-division and 50-division metric verniers each read 0.02 mm.
Smallest inside measurement without compensation · in: 0.250Starrett notes 0.250 inch (6.35 mm) of nib thickness is added for inside readings on its No. 123E&M; the inside vernier plate of the other Starrett calipers compensates automatically.

Made to

ISO 13385-1
DIN 862
ASME B89.1.14
JIS B.7507

Safety and care

Care

Starrett’s bulletin says to handle a vernier gage gently but firmly, never to force it, and to bring the movable surface close to the work by hand before using the fine adjusting nut.
Keep the work and measuring surfaces free of dirt and grit, wipe the gage after use and store it in its case with the clamp screws loosened.
Set the gage flat and well away from the bench edge when putting it down.
Check the zero periodically by bringing the nibs together and confirming that the zero lines on the beam and vernier plate align.
Use an occasional drop of precision instrument oil on the slides. Starrett says never to polish contact surfaces with emery cloth or to try to adjust the gage for wear, and that repairs are done at the factory.

Tips

Read the vernier by finding the one coincident line
On a 25-division inch vernier, count the inches, tenths and twenty-fifths on the beam to the vernier zero, then find the vernier line that coincides with a beam line and add its value in thousandths. Starrett’s own example reads 1.425 inch on the beam and adds 0.011 inch for the eleventh line, for 1.436 inch.1
Read outside from the left and inside from the right
Starrett’s caliper beam is graduated on both sides. Outside readings run left to right and inside readings right to left. With the jaws closed, the zero lines of the outside vernier plate coincide with the beam zero, while the inside plate zero falls several graduations beyond it, because that figure is the closed thickness of the nibs.1
Take inside readings directly on a compensated vernier
The width of both nibs must be included in every inside measurement. Starrett’s verniers compensate on the inside vernier plate, so inside readings are direct. Brown & Sharpe’s 1904 catalog, for its calipers without that feature, instructs the user to add a fixed allowance for the points when measuring inside.1 2
Lock the slide before taking the caliper off the work
Starrett’s procedure is to move the slide by hand until the jaws touch, tighten the clamp over the fine adjusting nut, turn the nut until the jaws engage firmly but not too tightly, then tighten the clamp over the vernier plate and carefully remove the caliper to take the reading.1
Use the divider centers to transfer a distance
Center points on the beam and slide let a divider or trammel point be set to the caliper’s reading for layout. Brown & Sharpe’s 1904 catalog describes the same feature, with points placed on the bars and slides so dividers can be set to transfer distances.1 2

History

Earliest documented

1631 (the vernier scale described); about 1830 (earliest dated vernier caliper in the collection sources read here)

Brussels (Vernier’s treatise, 1631); London (Holtzapffel and Company, about 1830)

Mitutoyo’s history reports that Pierre Vernier described vernier graduations in a book issued at Brussels in 1631. The Science Museum Group catalogs a vernier caliper for workshop use by Holtzapffel and Company, London, made about 1830, and vernier external callipers by the same firm dated 1800–1825. Mitutoyo’s history reports a vernier caliper made at a French Army artillery factory between 1837 and 1840 as the oldest in existence.1 2 3

The vernier is a way of dividing a scale, and it predates the caliper that made it common. Mitutoyo’s history traces the problem to Pedro Nunes’s 1542 scheme of concentric arcs with one fewer division on each, and to Pierre Vernier’s 1631 book, which it says described vernier graduations. The same history argues that what Vernier invented was probably only the graduation scheme, since sliding calipers were already in use and no caliper by him has been found, including at the Conservatoire National des Arts et Métiers. MacTutor, a university biography, gives a different account.

Before the vernier, a workshop measured with spring-joint calipers and a rule. Mitutoyo’s history says external and internal calipers could not make direct measurements and relied on a steel rule to read the opening afterward, so success depended on the user’s feel; vernier calipers allowed a dimension to be measured directly with good accuracy, and external and internal calipers are now practically obsolete although the principle is still used. The history adds that the vernier caliper has become so widespread that a tool with a sliding section carrying a vernier scale has become synonymous with the word caliper.

The vernier caliper took a workshop form between about 1800 and the middle of the century. The Science Museum Group holds Holtzapffel instruments from 1800–1825 and about 1830 that already read to a thousandth of an inch. Mitutoyo’s author reports that a French artillery factory caliper made in the 1837–1840 interval is the oldest in existence, and that J. W. Roe, who may not have known of it, wrote that Brown & Sharpe made the first vernier caliper in 1851. Mitutoyo’s author describes Brown’s graduating machine as the achievement that made accurate long scales possible.

Commercial supply made the form uniform. Brown & Sharpe’s own 1904 catalog says Joseph R. Brown began making steel rules in 1850, and its 1904 listing shows the features still sold today: a front scale with a vernier to thousandths, a back scale in 64ths, hardened and ground jaws serving inside and outside measurements, and points for setting dividers. Starrett’s 1975 bulletin describes the details of use, including a 25-division vernier of 0.001 inch and an inside plate that compensates for the nibs.

The vernier caliper has since been joined by the dial and digital caliper. Mitutoyo’s history dates the dial caliper to 1960 and the first digital calipers to 1977. Mitutoyo is itself a caliper manufacturer and the history is the company’s publication, so its priority claims are treated here as one account among several.

Timeline

1542
Pedro Nunes (Petrus Nonius) devises a scale of concentric quadrant arcs, each with one division fewer than the one outside it, to improve the astrolabe. Mitutoyo’s history describes it as a related but different scheme.1
1631
Pierre Vernier’s treatise La construction, l’usage, et les propriétés du quadrant nouveau de mathématiques is published at Brussels. Mitutoyo’s history says it describes vernier graduations; MacTutor says the book also describes a vernier caliper (see disputed).1 2
1800–1825
Holtzapffel and Co. of London make vernier external callipers of a triangular pattern with a sliding vernier scale, giving a magnification of 3.8 to 1 and reading to 0.001 inch, now in the Science Museum Group.1
about 1830
Holtzapffel and Company make a vernier caliper for workshop use, 29.5 cm long, cataloged by the Science Museum Group as an early vernier caliper.1
1837–1840
A vernier caliper with millimeter graduations and a vernier on the front face and pouce graduations on the back is made at a French Army artillery factory, dated by Mitutoyo’s author to the interval between the metric law of 4 July 1837 and its enforcement in 1840.1
1850
Joseph R. Brown of Providence begins to make steel rules; according to Mitutoyo, citing J. W. Roe, he builds an automatic linear graduating machine the same year.1 2
1851
Mitutoyo’s history, citing Roe, says Brown made the first vernier caliper reading to 1/1000 inch this year. The history adds that only four were made in the first year and that the instrument seems to have become saleable after about three years.1
1877
The first issue of American Machinist, in November, carries a Brown & Sharpe advertisement listing vernier calipers among its tools.1
1880
The L. S. Starrett Co. begins business and, according to Mitutoyo’s timeline, develops sliding and vernier calipers.1
1904
Brown & Sharpe’s catalog lists vernier calipers graduated to thousandths on the front and 64ths on the back, with hardened, ground jaws for inside and outside measurement, divider points on the bars and slides, and a version graduated in 1/50 millimeter.1
1960
Mauser-Messzeug and Helios of Germany develop dial calipers.1
1977
TESA develops a photoelectric incremental digital caliper, and Ingvar Andermo’s capacitance-type digital caliper is commercialized by C. E. Johansson.1
2011
ISO 13385-1, on the design and metrological characteristics of calipers, is instituted.1

Where the sources disagree

Did Pierre Vernier invent the vernier caliper or only the vernier scale?

His 1631 book describes his most famous invention, the vernier caliper.1
MacTutor, University of St Andrews
He described vernier graduations in the book, but no caliper by him has been found, and what he invented was probably only the graduation scheme.1
Mitutoyo’s history of calipers

When was Pierre Vernier born and when did he die?

Born 19 August 1584 at Ornans; died 14 September 1638 at Ornans.1
MacTutor
1580–1637.1
Mitutoyo’s history

Which is the earliest vernier caliper?

Brown & Sharpe made the first vernier caliper reading to 1/1000 inch in 1851; the company’s catalog stated for a time that Joseph R. Brown had invented it.1
J. W. Roe, as reported by Mitutoyo
A French Army artillery factory caliper made between 1837 and 1840 is the oldest in existence.1
Mitutoyo’s history
A vernier caliper for workshop use by Holtzapffel and Company was made in London about 1830.1
Science Museum Group (catalog record)

Gaps in the record (6)

Vernier’s 1631 text and a Brown & Sharpe source for the 1851 caliper have not been located; the 1851 date is known here only through Mitutoyo’s report of J. W. Roe.
The Science Museum Group’s Holtzapffel record gives a date and maker but no description of the scale; whether its vernier divides in tenths, fiftieths or otherwise is not stated in the record read.
The nib-allowance figure in Brown & Sharpe’s 1904 text is partly illegible in the scan, so no figure is quoted from it.
No sourced safety guidance was located.
No sourced independent test of caliper accuracy or of any buying criterion was located, so buying is null.
Standards: the slugs listed are candidates to be resolved; ISO 13385-1 is named by Mitutoyo, the others are assumed.