Chain (unit)

The is a  of  equal to 66 feet (22 yards). It is subdivided into 100 links or 4 rods. There are 10 chains in a, and 80 chains in one. In metric terms, it is 20.1168 m long. By extension, (running distance) is the distance along a curved or straight survey line from a fixed commencing point, as given by an.

The chain has been used for several centuries in England and in some other countries influenced by English practice. In the United Kingdom, there were 80 chains to the mile, but until the early nineteenth century the were longer than the statute mile; consequently a Scots chain was about 74 (imperial) feet, an Irish chain 84 feet. These longer chains became obsolete following the adoption of in 1824.

Definition
The UK statute chain is 22 yards, which is 66 feet. This unit is a in the United Kingdom, defined in the. One link is a hundredth part of a chain, which is 7.92 inch.

Origin
The surveyor’s chain was first mentioned 1579 and appears in an illustration in 1607. In 1593 the was redefined by a statute of  as 5,280 feet, to tie in with. In 1620, the  developed a method of accurately surveying land using a surveyor’s chain 66 feet long with 100 links. The 66 feet unit, which was four perches or rods, took on the name the chain. By 1675 it was accepted, and wrote: "...a Word or two of Dimensurators or Measuring Instruments, whereof the mosts usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the Englishs 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...'"

From, the chain and the 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. In 1784 wrote a report for the  proposing the ; it was adopted with some changes as the  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. "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.

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"

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