Editing Chain (unit)

{{Short description|Unit of length}}
{{Infobox unit
| name     = chain
| image = Gunter's chain at Campus Martius Museum.JPG
| caption = The chain is based on the length of Gunter's chain, which is {{convert|66|ft|yd}} long.
| standard = [[Imperial units|Imperial]]/[[US customary units|US]]&nbsp;units
| quantity = [[length]]
| symbol   = ch
| units1   = Imperial/US&nbsp;units
| inunits1 = {{val|22|u=[[Yard (unit)|yd]]}}, {{val|66|u=[[Foot (unit)|ft]]}}, {{val|100|u=[[Link (unit)|links]]}} 
| units2   = [[Metric system|Metric]] ([[SI]]) units
| inunits2 = {{convert|22|yd|m|4|lk=on|disp=out}}
}}

The '''chain''' (abbreviated '''ch''') is a [[Units of measurement|unit]] of [[length]] equal to 66 [[foot (unit)|feet]] (22 [[yard (unit of length)|yards]]), used in both the [[United States customary units|US customary]] and [[Imperial units|Imperial]] unit systems. It is subdivided into 100 [[Link (unit)|links]].<ref>{{cite book |title=Mathematics Dictionary |page= 453 |first1=Robert C. |last1=James |first2=Glenn |last2=James |isbn=9780412990410 |publisher=Chapman & Hall |location=New York |date=1992}}</ref><ref name="USNBS1960">{{cite book|title=Units of Weight and Measure (United States Customary and Metric): Definitions and Tables of Equivalents|url=https://nvlpubs.nist.gov/nistpubs/Legacy/MP/nbsmiscellaneouspub214.pdf|year=1960|publisher=U.S. Department of Commerce, National Bureau of Standards|pages=8–9|chapter=6 Tables of Interrelation of Units of Measurement}} (PDF)</ref> There are 10 chains in a [[furlong]], and 80 chains in one [[statute mile]].<ref name="USNBS1960" /> In metric terms, it is 20.1168&nbsp;[[metre|m]] long.<ref name="USNBS1960" /> By extension, '''chainage''' (running distance) is the distance along a curved or straight survey line from a fixed commencing point, as given by an [[odometer]].

The chain has been used since the early 17th century in England, and was brought by British settlers during the colonial period to other countries around the globe. In the United Kingdom, there were 80 chains to the mile, but until the early nineteenth century the [[Mile#British and Irish miles|Scottish and Irish customary miles]] were longer than the [[statute mile]]; consequently a Scots chain was about 74 (imperial) feet,<ref>{{cite book |author-link=John Smeaton |last=Smeaton |first=John |title=Reports of the Late John Smeaton, F.R.S. |date=1837 |publisher=M Taylor |location=London |page=[https://archive.org/details/reportslatejohn00smeagoog/page/n354 308] |edition=2nd |url=https://archive.org/details/reportslatejohn00smeagoog |quote=Since the foregoing Report [on the best route for the [[Forth and Clyde Canal]]] ... was delivered ... , Mr Smeaton has discovered that, notwithstanding the care and pains he took to be correct, he has committed an error, in supposing the Scotch chain, with which the measures of the length of the tract of land were taken, to consist of seventy feet each, whereas, in reality, it consists of seventy-four}}</ref> an Irish chain 84 feet. These longer chains became obsolete following the adoption of [[Imperial units|the imperial system of units]] in 1824.<ref>{{cite book |author1=William John Macquorn Rankine |author-link=William John Macquorn Rankine |title=A Manual of Civil Engineering |date=1863 |publisher=Griffin Bohn & Company |location=London |page=[https://archive.org/details/amanualcivileng05rankgoog/page/n368 3] |edition=2nd |url=https://archive.org/details/amanualcivileng05rankgoog}}</ref> In India, "metric chains" of exactly {{convert|20|metres|2|abbr=off}} are used, along with fractions thereof.<ref name=Punmia_etal />

==Definition==
The UK statute chain is 22 yards, which is {{convert|66|feet|4}}. This unit is a [[statute measure]] in the United Kingdom, defined in the [[Weights and Measures Act 1985]].<ref name=1985Act>
{{Cite web |title=Weights and Measures Act 1985 |url=http://www.legislation.gov.uk/ukpga/1985/72/schedule/1/part/VI |website=Legislation.gov.uk |access-date=25 September 2014 |at=Sch 1, Part VI }}</ref> One link is a hundredth part of a chain, which is {{convert| 7.92|inch|cm|4}}.<ref name=Rankine/>

The surveyor's chain first appears in an illustration in a Dutch map of 1607,<ref name="map">{{cite web |last1=Corneliisz van Alckmaer |first1=Pieter |title="Caerte vande gheleghentheyt van de Beemster met de landen die daeromme ende aengheleghen zijn, na rechte landmetersch conste op perfecte maet aldus ghestelt door Pieter Cornelisz. Cort van Alckmaer, ghesworen landmeter, anno 1607". Het Schermereiland met links een deel van de onbedijkte Schermer en rechts de onbedijkte Beemster. |url=https://www.regionaalarchiefalkmaar.nl/collecties/beelden/beelden-2/detail/9a5bede0-ce28-4584-9494-06c0abef1af9 |website=Regional Archive, Alkmaar |access-date=29 July 2018 |language=nl}}</ref> and in an English book for surveyors of 1610.<ref>{{cite encyclopedia |encyclopedia=Oxford English Dictionary |date=1933 |entry=Chain (5) |volume=2 |page=248 |url=https://archive.org/details/the-oxford-english-dictionary-1933-all-volumes/The%20Oxford%20English%20Dictionary%20Volume%202/page/248/mode/1up |quote=1610 W. F{{sc|olkingham}}, ''Art Survey.'' |title=The Oxford English Dictionary - 1933 - All Volumes }}</ref> In 1593 the [[Mile#English mile|English mile]] was redefined by a statute of [[Queen Elizabeth I]] as 5,280 feet, to tie in with [[Composition of Yards and Perches|agricultural practice]]. In 1620, the [[polymath]] [[Edmund Gunter]] developed a method of accurately surveying land using a surveyor's chain 66&nbsp;feet long with 100 links.<ref>{{cite web |title=Gunter biography |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Gunter.html |website=www-history.mcs.st-andrews.ac.uk |access-date=21 July 2018}}</ref> The 66-foot unit, which was four perches or rods,<ref name="Slater&Saunders">{{cite web |last1=Slater |first1=Michael |last2=Saunders |first2=Ian |title=Rods, poles and perches |url=http://www.northcravenheritage.org.uk/nchtjournal/Journals/2006/RodsPolesPerches/RodsPolesPerches.html |website=www.northcravenheritage.org.uk |publisher=North Craven Heritage Journal |access-date=29 July 2018}}</ref> took on the name the chain. By 1675 it was accepted, and [[John Ogilby|Ogilby]] wrote:
{{blockquote|
...a Word or two of Dimensurators or Measuring Instruments, whereof the most usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the English Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres...'<ref>{{cite book |title=Britannia  |chapter=Preface |chapter-url=https://www.fulltable.com/vts/m/map/ogilby/a/SH947.jpg |date=1675 |via=Fulltable.com}}</ref> |source=John Ogilby, ''[[Britannia (atlas)|Britannia]]'', 1675}}

From [[Gunter's chain|Gunter's system]], the chain and the [[Link (unit)|link]] became standard surveyors' units of length and crossed to the colonies. The thirteen states of America were expanding westward and the public land had to be surveyed for a [[cadastral]]. In 1784 [[Thomas Jefferson]] wrote a report for the [[Continental Congress]] proposing the [[Land Ordinance of 1785#History|rectangular survey system]]; it was adopted with some changes as the [[Land Ordinance of 1785]] on 20 May the following year. In the report, the use of the chain as a unit of measurement was mandated, and the chain was defined.<ref name="Cazier">{{cite web |last1=Cazier |first1=Lola |title=Surveys and Surveyors of the Public Domain 1785-1975 |url=https://www.ntc.blm.gov/krc/uploads/538/Sur_Sur_Pub_Dom.pdf |publisher=US Government |access-date=29 July 2018 |id=Stock Number 024-041-00083-6 |page=22}}</ref> 
<!-- This is a verbatim quote. Please do not "improve" by inserting other sources --> {{blockquote|1=
The chain is the unit of linear measurement for the survey of the public lands as prescribed by law. All returns of measurement in the rectangular system are made in the true horizontal distance in links, chains, and miles. The only exceptions to this rule are special requirements for measurement in feet in mineral surveys and townsite surveys.<ref name="Cazier" />

Linear Measurement
:1 Chain = 100 links or 66 feet
:1 Mile = 80 chains or 5,280 feet

Area Measurement
:1 Acre = 10 square chains or 43,560 square feet
:1 square mile = 640 acres
|source = Lola Cazier (1976), ''Surveys and Surveyors of the Public Domain 1785-1975'', page 15}}
<!-- Above is a verbatim quote. Please do not "improve" by inserting other sources -->

<!-- still we don't have a source that definitive says that: Gunter took the existing chain and modified it so it had 100 links measuring 4 perches in total so that it was 1/10 of a furlong, and tied the that to the existing acre measure. We don't know what his invention was – and there is no causal link between the instrument and the unit that appears to have been named after it-- help please if you have access to a hidden JSTOR PhD.b -->

==Modern use and historic cultural references==
{{further|Milestone|Linear referencing}}

===United Kingdom===
[[Image:Bridge miles and chains.jpg|thumb|Location marker painted on a British railway bridge, showing 112 miles and 63 chains; photograph taken August 2007]]
In the United Kingdom, the chain is no longer used for practical survey work.<ref>Plane and Geodetic Surveying, A.L. Johnson (SPON)</ref> However, it is still used on the railways as a location identifier. When railways were designed, the location of features such as bridges and stations was indicated by a cumulative longitudinal "mileage", using miles and chains, from a zero point at the origin or headquarters of the railway, or the originating junction of a new branch line. Since railways are linear in topology, the "mileage" or "chainage" is sufficient to identify a place uniquely on any given route. Thus, a given bridge location may be indicated as 112 miles and 63 chains (181.51&nbsp;km) from the origin. In the case of the photograph, the bridge is near [[Keynsham]], which is that distance from [[London Paddington station]]. The indication "MLN" after the mileage is the [[Engineer's Line Reference]] describing the route as the [[Great Western Main Line]], which is needed to uniquely determine the bridge, as there may be points at 112 miles 63 chains on other routes.

On new railway lines built in the United Kingdom such as [[High Speed 1]], the position along the alignment is still referred to as "chainage", although the value is now expressed in metres.<ref>[http://assets.dft.gov.uk/publications/hs2-maps-20120110/hs2arp00drrw05022issue4.pdf HS2 proposed alignment with chainages expressed in metres]</ref>

===North America===
The use of the chain was mandatory in laying out US townships.<ref name=Cazier/> A federal law was passed in 1785 (the [[Public Land Survey System|Public Land Survey Ordinance]]) that all official government surveys must be done with a Gunter's (surveyor's) chain. Chains and links are commonly encountered in older [[metes and bounds]] legal descriptions. Distances on township [[plat]] maps made by the US General Land Office are shown in chains.

Under the US [[Public Land Survey System]], [[Lot (real estate)|parcels of land]] are often described in terms of the [[Section (United States land surveying)|section]] ({{convert|640|acre|ha|0|disp=or}}), quarter-section ({{convert|160|acre|ha|1|disp=or}}), and quarter-quarter-section ({{convert|40|acre|ha|2|disp=or}}). Respectively, these square divisions of land are approximately 80 chains (one mile or 1.6&nbsp;km), 40 chains (half a mile or 800&nbsp;m), and 20 chains (a quarter mile or 400&nbsp;m) on a side.

The chain is still used in agriculture: measuring wheels with a circumference of 0.1 chain (diameter ≈ 2.1&nbsp;ft or 64&nbsp;cm) are still readily available in Canada and the United States. For a rectangular tract, multiplying the number of turns of a chain wheel for each of two adjacent sides and dividing by 1,000 gives the area in acres.

In Canada, road allowances were originally 1 chain wide and are now 20 metres.<ref>{{cite news |last1=Lakey |first1=Jack |title=Turns out there is a standard to determine where a homeowner's property ends: The Fixer |url= https://www.thestar.com/yourtoronto/the_fixer/2017/06/21/turns-out-there-is-a-standard-to-determine-where-a-homeowners-property-ends-the-fixer.html |access-date=22 June 2017 |work=[[Toronto Star]] |date=21 June 2017}}</ref>

The unit was also used in mapping the United States along train routes in the 19th century. [[Railroad]]s in the United States have long since {{when|date=July 2018}} used [[decimal]] fractions of a mile. Some subways such as the [[New York City Subway]] and the [[Washington Metro]] were designed with and continue with a [[New York City Subway chaining|chaining system]] using the 100-foot [[engineer's chain]].<ref name=ERA>{{Cite web|url=https://issuu.com/erausa/docs/2017-01-bulletin|title=The ERA Bulletin 2017-01|date=January 18, 2017|website=[[Issuu]]|publisher=Electric Railroaders' Association|access-date=January 18, 2017}}</ref>

In the United States, the chain is also used as the measure of the rate of spread of wildfires (chains per hour), both in the predictive [[National Fire Danger Rating System]] as well as in after-action reports. The term ''chain'' is used by wildland firefighters in day-to-day operations as a unit of distance.<ref>[http://www.fs.fed.us/psw/publications/documents/psw_gtr090/psw_gtr090.pdf Documents]</ref>

===Australia and New Zealand===
In [[Australia]] and [[New Zealand]], most building lots in the past were a quarter of an acre, measuring one chain by two and a half chains, and other lots would be multiples or fractions of a chain.<ref name="Seddon1998">{{cite book|author=George Seddon|title=Landprints: Reflections on Place and Landscape|url=https://books.google.com/books?id=ZIAR6EvER2AC&pg=PA151|access-date=28 May 2013|date=28 September 1998|publisher=Cambridge University Press|isbn=978-0-521-65999-4|pages=151–}}</ref> The street [[frontage]]s of many houses in these countries are one chain wide—roads were almost always {{convert|1|chain|m|1}} wide in urban areas,<ref name="Seddon1998"/> sometimes {{convert|1.5|chain|m|1}} or {{convert|2.5|chain|m|1}}. Laneways would be half a chain (10.1&nbsp;m). In rural areas the roads were wider, up to {{convert|10|chain|m|1}} where a [[stock route]] was required. {{convert|5|chain|m|1}} roads were surveyed as major roads or highways between larger towns, {{convert|3|chain|m|1}} roads between smaller localities,<ref>{{cite web|last=Lay|first=M. G.|title=Roads|url=http://www.emelbourne.net.au/biogs/EM01255b.htm|work=emelbourne the city past and present|publisher=School of Historical Studies Department of History, The University of Melbourne|access-date=28 May 2013|date=July 2008}}</ref> and {{convert|2|chain|m|1}} roads were local roads in farming communities. Roads named Three Chain Road etc. persist today.<ref>{{cite web |title=375 THREE CHAIN ROAD, Kilmore, Vic 3764 - Property Details |url=https://www.realestate.com.au/sold/property-livestock-vic-kilmore-7908210 |website=www.realestate.com.au |access-date=8 August 2018 |language=en-AU}}</ref><ref>{{cite web |title=Map of Three Chain Road in Queensland - Bonzle Digital Atlas of Australia |url=http://www.bonzle.com/c/a?a=p&p=173789&cmd=sp |website=www.bonzle.com |access-date=8 August 2018}}</ref>

The "Queen's Chain" is a concept that has long existed in New Zealand, of a strip of public land, usually 20 metres (or one chain in pre-metric measure) wide from the high water mark, that has been set aside for public use along the coast, around many lakes, and along all or part of many rivers.<ref>{{cite web|url=https://en.oxforddictionaries.com/definition/queen%27s_chain|archive-url=https://web.archive.org/web/20180808172201/https://en.oxforddictionaries.com/definition/queen%27s_chain|url-status=dead|archive-date=August 8, 2018|access-date=4 July 2017|title=Queen's Chain|publisher=Oxford Dictionaries – oxforddictionaries.com}}</ref><ref>{{cite web|url=http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=3517579|access-date=4 July 2017|title=Truth behind the Queen's Chain|date=12 August 2003|publisher=[[The New Zealand Herald]] }}</ref> These strips exist in various forms (including road reserves, esplanade reserves, esplanade strips, marginal strips and reserves of various types) but not as extensively and consistently as is often assumed.<ref>{{Cite web|url=http://www.teara.govt.nz/en/law-of-the-foreshore-and-seabed/page-3|title=Te Ara, Encyclopedia of New Zealand}}</ref>

===Cricket pitches===
The chain also survives as the length of a [[cricket pitch]], being the distance between the stumps.<ref>{{cite web|url=https://www.espncricinfo.com/story/_/id/23233624/the-measurements-cricket |title=The measurements of cricket |work=ESPN Cricinfo |access-date=19 February 2020}}</ref><ref>{{cite web|url=https://www.bbc.co.uk/bitesize/guides/zpcg4j6/revision/2 |title=Cricket - factfile |work=BBC Bitesize |access-date=19 February 2020}}</ref>

==Measuring instruments==
Civil engineers and surveyors use various instruments including chains to measure distance.<ref name=Punmia_etal>{{cite book |last1=Punmia |first1=B. C. |last2=Jain |first2=A. K. |last3=Jain |first3=A. K. |year=2003 |title=Basic civil engineering |publisher=Laxmi Publications |location=New Delhi |isbn=9788170084037 |oclc=1006316184}}</ref> Other instruments used for measuring distance include tapes and bands. A steel band is also known as a "band chain".<ref>[https://theconstructor.org/surveying/types-of-chains-surveying/13889/ Types of Chains used in Surveying, Their Parts, Testing and Advantages]</ref>

===Surveyors' chain (Gunter's chain) ===
{{main|Gunter's chain}}
{{anchor|Gunter's chain}} <!-- maybe incoming redirections-->
In 1620, the polymath [[Edmund Gunter]] developed a method of accurately surveying land using a 100 link chain, 22 yards (66 feet) long, called the [[Gunter's Chain]]. [[Gunter's chain#Similar measuring chains|Other surveyors chains]] have been used historically.

=== Engineer's chain (Ramsden's chain)===
{{anchor|Ramsden's chain (engineer's chain)}}
{{main|Ramsden surveying instruments#Chains and rods}}
A longer chain of {{convert|100|ft|m|1}}, with a hundred {{convert|1|ft|mm|0}} links, was devised in the UK in the late 18th century by [[Ramsden surveying instruments|Jesse Ramsden]], though it never supplanted Gunter's chain.<ref name=Rankine>{{cite book |author1=William John Macquorn Rankine |author-link=William John Macquorn Rankine |title=A Manual of Civil Engineering |date=1863 |publisher=Griffin Bohn & Company |location=London |pages=[https://archive.org/details/amanualcivileng05rankgoog/page/n38 18]–19 |edition=2nd |url= https://archive.org/details/amanualcivileng05rankgoog}}</ref> Surveyors also sometimes used such a device, and called it the ''engineer's chain''.<!-- The term ''chain'' in this case usually refers to the measuring instrument rather than a unit of length, and distances measured are normally given in feet and decimal fractions of a foot (not inches).{{citation needed|date=July 2018}} A lot of these references refer to the manufacturing process used to increase the accuracy of an existing precision instrument- you had to solve heat expansion, twisting, and wear from friction. Also important was the design of the handle and whether it incorporated an adjustment screw. This is mainly supported by Rankine. The Rankine ref does not mention Ramsden- so thats another factoid to remove. Look to [[Anglo-French Survey (1784–1790)]] for a better reference. Indeed [[Gunter's chain#Similar measuring chains]] will be a useful starting point when it has been verified- for example Ramsden was British not American. See also:

[http://www.clintoncountyohgis.org/units_of_measure.htm Clinton is one of the many sites that copies from US government Glossary of Surveying and Mapping Terms]
[http://www.cdscapes.com/reading-property-surveys.html Charlotte dreamspace is another]-->

==={{lang|es|Vara|nocat=y}} or Texas chain===
In the [[Southwestern United States]], the ''{{lang|es|vara}} chain'' also called the ''Texas chain'', of 20 {{lang|es|[[Spanish customary units#Vara (unit of length)|varas]]}} ({{cvt|16.9164|m|ft|1}}) was used in surveying [[Viceroyalty of New Spain|Spanish]] and later [[First Mexican Republic|Mexican]] land grants, such as the major [[Fisher–Miller Land Grant|Fisher–Miller]] and [[Paisano Grant]]s in Texas, [[Land grants in New Mexico|several similarly large ones in New Mexico]], and [[Ranchos of California|over 200 smaller {{lang|es|ranchos|nocat=y}} in California]].

===Metric chains===
Metric chains, of lengths 5&nbsp;m, 10&nbsp;m, 20&nbsp;m and 30&nbsp;m, are widely used in India.<ref name=Punmia_etal /> Tolerances are ±3&nbsp;mm for 5&nbsp;m and 10&nbsp;m chains, ±5&nbsp;mm for a 20&nbsp;m chain, and ±8&nbsp;mm for a 30&nbsp;m chain.<ref>{{cite book |last=Bhavikatti |first=S. S. |year=2008 |title=Surveying and levelling |volume= 1 |publisher=IK International |location=New Delhi |isbn=9788190694209 |oclc=660131493 |chapter=Chain Surveying}}</ref>

====Revenue chain====
In India, a revenue chain with 16 links and of length {{cvt|33|ft|disp=flip}} is used in [[Cadastral surveying|cadastral surveys]].<ref>[http://www.agriinfo.in/default.aspx?page=topic&superid=8&topicid=45 Instruments used in Surveying - Instruments Used for Measuring Distance]</ref>

===Other instruments===
Also in North America, a variant of the chain is used in [[forestry]] for [[Traverse (surveying)|traverse surveys]].{{citation needed|date=July 2018}} This modern chain is a static cord (thin rope) 50 metres long, marked with a small tag at each metre, and also marked in the first metre every [[decimetre]].{{citation needed|date=July 2018}} When working in dense bush, a short [[Axe#Axes designed to cut or shape wood|axe]] or [[hatchet]] is commonly tied to the end of the chain, and thrown through the bush in the direction of the traverse.{{clarify|date=July 2018|reason=What is it called?}}

Another version used extensively in [[forestry]] and [[surveying]] is the ''hip-chain'': a small box containing a string counter, worn on the hip.{{citation needed|date=July 2018}} The user ties off the spooled string to a stake or tree and the counter tallies distance as the user walks away in a straight line. These instruments are available in both [[Foot (unit)|feet]] and [[metre]]s.

==Use in popular culture==
The lyrics of [[Three Chain Road]], by [[Lee Kernaghan]], include the line "He lived out on the three chain road" which is the name of many Australian roads; referring to the width of the road reserve.<ref>[https://genius.com/Lee-kernaghan-three-chain-road-lyrics Lee Kernaghan - Three Chain Road lyrics]</ref>

==References==
{{Reflist}}

==External links==
*{{usurped|1=[https://web.archive.org/web/20100618055137/http://pballew.net/arithm16.html#gunter Math Words]}}

{{Forestry tools}}
{{Imperial units}}
{{United States Customary Units}}

[[Category:Units of length]]
[[Category:Imperial units]]
[[Category:Surveying]]
[[Category:Customary units of measurement in the United States]]
[[Category:Forestry tools]]