Gunter's chain

See also: Ramden’s chain and the Rathborn chain.

Various units of length used for surveying in the English-speaking world, all consisting of 100 links. The surveyor’s chain of 100 links is identified with Edmund Gunter, who introduced such a chain in 1620, although chains divided decimally had existed earlier. The convenience of this decimal division was the cause of the chain's success; among other advantages, an area 1 chain by 10 chains was an acre.

The abbreviation is “ch”.

1

When “Gunter's chain” is used without qualification, and always in the United States, the unit is (17th century – present), = 1⁄10 furlong = 4 perches= 22 yards = 66 feet = 20.1168 meters. All these units are based upon the survey foot, not the international foot. A square chain = 4,356 square feet (approximately 404.686 square meters). One link = 7.92 inches, a hundredth of a rod.

The square link is a unit of area, = 62.75 square inches (404.686 square centimeters).

sources

THE CHAIN-- There are two kinds of chain in common use, the Surveyor’s (or Gunter’s) Chain, and the Engineer’s Chain. Gunter’s chain is 66 feet long, and its use is confined chiefly to land surveying on account of its simple relation to the acre and to the mile.
1 Gunter's Chain = 4 Rods = 100 Links
1 Mile = 80 Chains
1 Acre = 10 Square Chains
Evidently each link is 66/100 of a foot (or 7.92 inches) long. The inch, however, is never used in surveying fieldwork.

The engineer’s chain is 100 feet long and is divided into one hundred links of one foot each. Each end link is provided with a handle, the outside of which is the zero point, or end, of the chain. In these chains, every tenth link counting from either end is marked by a brass tag having one, two three, or four points corresponding to the number of tens which it marks. The middle of the chain is marked by a round tag. In the engineer's chain then the 10-ft. and 90-ft. points, the 20-ft. and 80-ft points, etc., are marked alike; hence it is necessary to observe on which side of the 50-ft. point a measurement falls in order to read the distance correctly. Distances measured with the surveyor’s chain are recorded as chains and links, (or in chains and decimals); while those measured with the engineer's chain are recorded as feet and decimals.

On account of the large number of wearing surfaces and the consequent lengthening with use, the chain should be frequently compared with a standard of length ... It may be adjusted to agree with the standard, by means of a nut at the handle, which allows the length of the chain to be altered by lengthening or shortening the end link.

Charles B. Breed and George L. Hosmer.
The Principles and Practice of Surveying. Vol 1. 3rd edition.
New York: John Wiley & Sons, 1908.

The simplest of these [types of survey] is the "Chain Survey," but this is only suitable for moderately small areas. The chief appliances used are the chain, tape, arrows, ranging rods, offset staff, and occasionally a cross staff, optical square, box-sextant, or prismatic compass. The Chain is generally divided into 100 links, sometimes into 50- but there are several varieties and lengths in ordinary use. The links are composed of lengths of iron or steel wire, and—except at the centre of the chain, and at the 25th link from each end, where swivel joints (S, Fig. 2) are provided—these are connected at their extremities by three small oval rings, preferably welded. At every 10th link from each end of the chain a brass tag or teller is fastened to the small central connecting ring. The teller which has only one point indicates ten links from either end of the chain—i.e. the 10th or the 90th link measuring in the same direction; that with two points marks the 20th or the 80th link ; three points indicate the 30th or the 70th link; four points the 40th or the 60th link; and a circular tag the centre of the chain. The brass tellers are sometimes designed to be inserted in the length of the chain, but though less liable to catch in hedges, etc., they are perhaps hardly as distinctive as the usual type. The ends of the chain are furnished with brass handles attached by means of swivel joints, and the length of 100 links is measured from the outside of one handle to the outside of the other.

drawing of chain showing tellers

The Gunter’s chain—so named after its inventor—is generally used by the Land Surveyor. It is 66 ft. in length, each link measuring 7.92", and is very convenient when it is required to calculate areas in acres and decimals of an acre, since 10 sq. chains = 1 acre : also when linear dimensions are required in miles and furlongs, since 10 chains = 1 furlong and 80 chains =. 1 mile. When the term “chain” or “link” is used in a general sense, without reference to any particular unit of measurement, the Gunter's chain is inferred.

The Engineer's chain is 100 ft. long, each link being 1 ft. in length. It is heavier than the Gunter's chain, but being longer does not need to be laid down so frequently in the measurement of a definite distance; for this reason there is less liability to error from the inaccurate marking of the ends of the chain. Again, as the levelling staff is usually graduated in feet and decimal parts of a foot, this chain is more convenient than the 66 ft. chain when used in connection with levelling or tacheometric operations. In municipal work, too, the 100 ft. chain is employed, as, in this case, dimensions are required to be expressed in yards, feet, and inches.

Metre chains are also in use, the commonest lengths being 10, 20, and 25 metres. They are subdivided into one-fifth parts of a metre and tallied at every two metres from each end.

W. Norman Thomas.
Surveying.
London: Edward Arnold, 1920.

2

In Scotland, Gunter's chain, still of 100 links, was 4 falls long = 74 feet (= 22.5552 meters). The link was 8.88 inches.

Through a misdefining in the mathematical literature of the Scots ell and consequently of the fall, beginning with Colin McLaurin’s comments in an edition of 1745 of David Gregory’s Treatise of Practical Geometry, the Scots chain came to be described in print as 74.4 feet long. It is not known if this length was actually used by surveyors. The matter is discussed in Connor and Simpson.

3

In Ireland, a link of Gunter’s chain, again of 100 links, was 10.08 inches. This value adapted it to the Irish acre.