Gunter's chain (also known as Gunter's measurement) is a distance-measuring device used for

surveying Surveying or land surveying is the technique, profession, art, and science of determining the land, terrestrial Plane (mathematics), two-dimensional or Three-dimensional space#In Euclidean geometry, three-dimensional positions of Point (geom ...

. It was designed and introduced in 1620 by English clergyman and mathematician Edmund Gunter (1581–1626). It enabled plots of land to be accurately surveyed and plotted, for legal and commercial purposes. Gunter developed an actual measuring chain of 100 links. These, the chain and the link, became statutory measures in England and subsequently the

British Empire The British Empire comprised the dominions, Crown colony, colonies, protectorates, League of Nations mandate, mandates, and other Dependent territory, territories ruled or administered by the United Kingdom and its predecessor states. It bega ...

Description

The chain is divided into 100 links, usually marked off into groups of 10 by brass rings or tags which simplify intermediate measurement. Each link is thus long. A quarter chain, or 25 links, measures and thus measures a rod (or pole). Ten chains measure a

furlong A furlong is a measure of distance in imperial units and United States customary units equal to one-eighth of a mile, equivalent to any of 660 foot (unit), feet, 220 yards, 40 rod (unit), rods, 10 chain (unit), chains, or a ...

and 80 chains measure a

statute mile The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of length; both are based on the older English unit of length equal to 5,280 English ...

. Gunter's chain reconciled two seemingly incompatible systems: the traditional English land measurements, based on the number four, and decimals based on the number 10. Since an

acre The acre ( ) is a Unit of measurement, unit of land area used in the Imperial units, British imperial and the United States customary units#Area, United States customary systems. It is traditionally defined as the area of one Chain (unit), ch ...

measured 10 square chains in Gunter's system, the entire process of land area measurement could be computed using measurements in chains, and then converted to acres by dividing the results by 10. Hence 10 chains by 10 chains (100 square chains) equals 10 acres, 5 chains by 5 chains (25 square chains) equals 2.5 acres. By the 1670s the chain and the link had become statutory units of measurement in England.

Method

The method of

a field or other parcel of land with Gunter's chain is to first determine corners and other significant locations, and then to measure the distance between them, taking two points at a time. The surveyor is assisted by a chainman. A ranging rod (usually a prominently coloured wooden pole) is placed in the ground at the destination point. Starting at the originating point the chain is laid out towards the ranging rod, and the surveyor then directs the chainman to make the chain perfectly straight and pointing directly at the ranging rod. A pin is put in the ground at the forward end of the chain, and the chain is moved forward so that its hind end is at that point, and the chain is extended again towards the destination point. This process is called ranging, or in the US, chaining; it is repeated until the destination rod is reached, when the surveyor notes how many full lengths (chains) have been laid, and he can then directly read how many links (one-hundredth parts of the chain) are in the distance being measured. The chain usually ends in a handle which may or may not be part of the measurement. An inner loop (visible in the NMAH photograph) is the correct place to put the pin for some chains. Many chains were made with the handles as part of the end link and thus were included in the measurement. The whole process is repeated for all the other pairs of points required, and it is a simple matter to make a scale diagram of the plot of land. The process is surprisingly accurate and requires only very low technology. Surveying with a chain is simple if the land is level and continuous—it is not physically practicable to range across large depressions or significant waterways, for example. On sloping land, the chain was to be "leveled" by raising one end as needed, so that undulations did not increase the apparent length of the side or the area of the tract.

Unit of length

Although link chains were later superseded by the steel ribbon tape (a form of

tape measure A tape measure or measuring tape is a long, flexible ruler used to measure length or distance. It usually consists of a ribbon of cloth, plastic, fibreglass, or metal (usually - hard steel alloy) strip with linear measurement markings. Types Ta ...

), its legacy was a new statutory unit of length called the chain, equal to 22 yards (66 feet) of 100 links. This unit still exists as a location identifier on British railways, as well as all across America in what is called the public land survey system. In the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

(US), for example, Public Lands Survey plats are published in the chain unit to maintain the consistency of a two-hundred-year-old database. In the Midwest of the US it is not uncommon to encounter deeds with references to chains, poles, or rod units, especially in farming country. Minor roads surveyed in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

and

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

in the 19th and early 20th centuries are customarily one chain wide. The length of a

cricket pitch A cricket pitch is the rectangular central strip of a cricket field between the two wickets, where most of the action takes place. It is long (1 Chain (unit), chain) and wide. The surface is flat and is normally covered with extremely sh ...

is one chain (22 yards).

Similar measuring chains

A similar American system, of lesser popularity, is '' Ramsden's'' or the ''engineer's system'', where the chain consists also of 100 links, each one

foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...

(0.3048 m) long. The original of such chains was that constructed, to very high precision, for the measurement of the baselines of the Anglo-French Survey (1784–1790) and the Principal Triangulation of Great Britain. The even less common ''Rathborn system'', also from the 17th century, is based on a 200-link chain of two rods (33 feet, 10.0584 m) length. Each rod (or perch or pole) consists of 100 links, (1.98 inches, 50.292 mm each), which are called ''seconds'' (), ten of which make a ''prime'' (, 19.8 inches, 0.503 m). Vincent Wing made chains with 9.90-inch links, most commonly as 33-foot half-chains of 40 links. These chains were sometimes used in the American colonies, particularly Pennsylvania. In

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

, surveying chains (occasionally 30 metres) in length are used. Links are long. In France after the French Revolution, and later in countries that had adopted the

Metric System The metric system is a system of measurement that standardization, standardizes a set of base units and a nomenclature for describing relatively large and small quantities via decimal-based multiplicative unit prefixes. Though the rules gover ...

, 10-metre (32 ft 9.7 in) chains, of 50 links each long were used until the 1950s.Plomion, Charles. Arithmétique-Cours élémentaire, Librairie A. Hatier, Paris, 1925

References

External links