Editing Micrometer (device) (section)

==Operating principles==

[[File:Micrometer no zero error.gif|thumb|Animation of a micrometer in use. The object being measured is in black. The measurement is 4.140&nbsp;±&nbsp;0.005&nbsp;mm.]]
Micrometers use the screw to transform small distances<ref name="Loo Kang 2014">* {{Citation
|last1 = Loo Kang 
|first1 = Wee
|last2 = Hwee Tiang
|first2 = Ning
|year = 2014
|title = Vernier caliper and micrometer computer models using Easy Java Simulation and its pedagogical design feature-ideas to augment learning with real instruments
|arxiv=1408.3803
|doi=10.1088/0031-9120/49/5/493
|journal=[[Physics Education]] |volume=49 |number=5 
|page = 493
|bibcode=2014PhyEd..49..493W
|s2cid = 119243007
}}</ref> (that are too small to measure directly) into large rotations of the screw that are big enough to read from a scale. The accuracy of a micrometer derives from the accuracy of the thread-forms that are central to the core of its design. In some cases it is a [[differential screw]]. The basic operating principles of a micrometer are as follows:
# The amount of rotation of an accurately made screw can be directly and precisely correlated to a certain amount of axial movement (and vice versa), through the constant known as the screw's ''[[screw thread#Lead, pitch, and starts|lead]]'' ({{IPA|/ˈliːd/}}). A screw's ''lead'' is the distance it moves forward axially with one complete turn (360[[Degree (angle)|°]]). (In most threads [that is, in all single-start threads], ''lead'' and ''pitch'' refer to essentially the same concept.)
# With an appropriate lead and major diameter of the screw, a given amount of axial movement will be ''amplified'' in the resulting circumferential movement.

For example, if the lead of a screw is 1&nbsp;mm, but the major diameter (here, outer diameter) is 10&nbsp;mm, then the circumference of the screw is 10π, or about 31.4&nbsp;mm. Therefore, an axial movement of 1&nbsp;mm is amplified (magnified) to a circumferential movement of 31.4&nbsp;mm. This amplification allows a small difference in the sizes of two similar measured objects to correlate to a larger difference in the position of a micrometer's thimble. In some micrometers, even greater accuracy is obtained by using a [[differential screw]] adjuster to move the thimble in much smaller increments than a single thread would allow.<ref>{{US patent reference
 | number = 343478
 | y = 1880
 | m = 02
 | d = 08
 | inventor = McArthur, Duncan
 | title = Micrometer Calipers
}}</ref><ref>{{cite book |author=M.M. Lanz & Betancourt, translated from the original French |date=1817 |title=Analytical essay on the construction of machines |publisher=R. Ackermann |location=London |pages=14–15, 181 Plate 1 fig D3}}</ref><ref name="Mitutoyo">{{cite web |title=Micrometer Heads Series 110-Differential Screw Translator(extra-Fine Feeding) Type |work=Product Catalog |publisher=Mitutoyo, U.S.A. |url=http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1560 |access-date=December 11, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20111109164636/http://www.mitutoyo.com/TerminalMerchandisingGroup.aspx?group=1560 |archive-date=November 9, 2011 }}</ref>

In classic-style analog micrometers, the position of the thimble is read directly from scale markings on the thimble and sleeve (for names of parts see next section). A [[vernier scale]] is often included, which allows the position to be read to a fraction of the smallest scale mark. In digital micrometers, an electronic readout displays the length digitally on an [[LCD]] on the instrument. There also exist mechanical-digit versions, like the style of car [[odometer]]s where [[:File:Odometer2.jpg|the numbers "roll over"]].