Category:Units of length
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Pages in category "Units of length"
The following 149 pages are in this category, out of 149 total, this list may not reflect recent changes (learn more).
|Wikimedia Commons has media related to Units of length.|
The following 149 pages are in this category, out of 149 total, this list may not reflect recent changes (learn more).
1. Unit of length – A Unit of length refers to any discrete, pre-established length or distance having a constant magnitude which is used as a reference or convention to express linear dimension. The most common units in use are U. S. customary units in the United States. British Imperial units are used for some purposes in the United Kingdom. The metric system is sub-divided into SI and non-SI units, the base unit in the International System of Units is the metre, defined as the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second. It is approximately equal to 1.0936 yards, other units are derived from the metre by adding prefixes from the table below, For example, a kilometre is 1000 metres. In the Centimetre–gram–second system of units, the unit of length is the centimetre. Other non-SI units are derived from decimal multiples of the metre, the basic unit of length in the Imperial and U. S. customary systems is the yard, defined as exactly 0.9144 m by international treaty in 1959. Common Imperial units and U. S. astronomical unit AU, approximately the distance between the Earth and Sun. Light-year ly ≈9460730472580.8 km The distance that light travels in a vacuum in one Julian year and this is often a characteristic radius or wavelength of a particle. A Measure of All Things, The Story of Man and Measurement
2. Astronomical unit – The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
3. Barleycorn (unit) – The barleycorn is a small English unit of length equal to 1⁄3 of an inch still used in Great Britain and Ireland as a determiner of shoe sizes. The notion of three barleycorns composing an inch certainly predates this statute, however, appearing in the 10th-century Welsh Laws of Hywel Dda. In practice, various weights and measures acts of the English kings were standardized with reference to some particular yard-length iron, brass, the formal barleycorn was 1/108 of its length. The English statute notwithstanding, the barleycorn was also taken as a measure of length equal to 1/4 inch. British and Irish shoe sizes differ from one another by the distance of a barleycorn, as modern studies show, the actual length of a kernel of barley varies from as short as 4–7 mm to as long as 12–15 mm depending on the cultivar. Older sources claimed the length of a grain of barley being 0.345 in. Line, 1/4 of a barleycorn or 1/12 of an inch poppyseed, 1/4 or 1/5 of a barleycorn
4. Caliber – In guns, particularly firearms, caliber or calibre is the approximate internal diameter of the barrel, or the diameter of the projectile it fires, in hundredths or sometimes thousandths of an inch. For example, a 45 caliber firearm has a diameter of.45 of an inch. Barrel diameters can also be expressed using metric dimensions, as in 9mm pistol, when the barrel diameter is given in inches, the abbreviation cal can be used. Good performance requires a bullet to closely match the diameter of a barrel to ensure a good seal. While modern cartridges and cartridge firearms are referred to by the cartridge name. Firearm calibers outside the range of 17 to 50 exist, but are rarely encountered. Larger calibers, such as.577.585.600.700, the.950 JDJ is the only known cartridge beyond 79 caliber used in a rifle. Referring to artillery, caliber is used to describe the length as multiples of the bore diameter. A 5-inch 50 calibre gun has a diameter of 5 in. The main guns of the USS Missouri are 1650 caliber, makers of early cartridge arms had to invent methods of naming the cartridges, since no established convention existed then. One of the early established cartridge arms was the Spencer repeating rifle, later various derivatives were created using the same basic cartridge, but with smaller-diameter bullets, these were named by the cartridge diameter at the base and mouth. The original No.56 became the. 56-56, and the smaller versions. 56-52. 56-50, the. 56-52, the most common of the new calibers, used a 50-cal bullet. Optionally, the weight in grains was designated, e. g. 45-70-405. Variations on these methods persist today, with new cartridges such as the.204 Ruger, metric diameters for small arms refer to cartridge dimensions and are expressed with an × between the bore diameter and the length of the cartridge case, for example,7. 62×51 NATO. This indicates that the diameter is 7. 62mm, loaded in a case 51mm long. Similarly, the 6. 5×55 Swedish cartridge has a diameter of 6.5 mm. An exception to rule is the proprietary cartridge used by U. S. maker Lazzeroni. The following table lists commonly used calibers where both metric and imperial are used as equivalents
5. Caliber (artillery) – In artillery, caliber or calibre is the internal diameter of a gun barrel, or by extension a relative measure of the length. Rifled barrels introduce ambiguity to measurement of caliber, a rifled bore consists of alternating grooves and lands. The distance across the bore from groove to groove is greater than the distance from land to land, the depth of rifling grooves increases in larger calibers. United States Navy guns typically used rifling depth between one-half and one percent of caliber, projectile bourrelet diameter specification was 0.015 inches less than land to land diameter with a minus manufacturing tolerance so average clearance was about 0.012 inches. Driving band diameter was groove to groove diameter plus 0.02 inches, the length of the barrel is often quoted in calibers. For example, US Naval Rifles 3 in or larger, the effective length of the barrel is divided by the barrel diameter to give a dimensionless quantity.81 As an example, the main guns of the Iowa-class battleships can be referred to as 16/50 caliber. They are 16 inches in diameter and the barrel is 800 inches long, the bore to barrel length ratio is called caliber in naval gunnery,81 but is called length in army artillery. Before World War II, the US Navy used 5/51 caliber as surface-to-surface guns, by the end of World War II, the dual purpose 5/38 caliber was standard naval armament against surface and air targets. All three had a diameter of 5 inches. At sea, a weapon had to perform, without fail, there was no ready replacement, nor one that could be readily supplied. Over time, the terms of pound and bore became confused and blurred, eventually, when the technology existed, the bore came to be the standard measure. For naval rifles, the change was to actual bore. They then began to measure the length of the weapon in calibers. These were a measure of the bore of the barrel versus the rifled bore of the barrel. In other words, a 12/45 is 12×45= the length of the bore of that gun in inches. This explains the differences in both penetration and long range performance of naval rifles over the years. In addition to the improvements in overall performance, the increase in barrel length also allowed, in some circumstances. For example, the American 14/45, as introduced in the New York-class battleships, later improvements to the design, lengthening the rifle itself and also altering the breech, allowed a 1400 lb. projectile and, overall, a greater barrel life
6. Chain (unit) – A chain is a unit of length. It measures 66 feet, or 22 yards, or 100 links, there are 10 chains in a furlong, and 80 chains in one statute mile. An acre is the area of 10 square chains, the chain has been used for several centuries in Britain and in some other countries influenced by British practice. By extension, chainage is the distance along a curved or straight line from a fixed commencing point. The chain was used with the mile to indicate land distances. Starting in the 19th century, the chain was used as a subdivision with the mile to show distances between stations, tunnels and bridges. The locally used units were often inconsistent from place to place, a rectangle of land one furlong in length and one chain in width has an area of one acre. His chain had 100 links, and the link is used as a subdivision of the chain as a unit of length, american surveyors sometimes used a longer chain of 100 feet, also of 100 links, known as the engineers chain or Ramsdens chain. The first such was constructed by Jesse Ramsden for the measurement of the Hounslow baseline at the start of the Anglo-French Survey. The term chain in this usually refers to the measuring instrument rather than a unit of length. Also in North America a modern variant of the chain as a tool is used in forestry for traverse surveys and this modern chain is a static cord,50 metres long, marked with a small tag at each metre, and also marked in the first metre every decimetre. When working in dense bush, an axe or hatchet is commonly tied to the end of the chain. Another version used extensively in forestry and surveying is the hip-chain, a hip-chain is a small box containing a string meter, worn on the hip. The user simply ties the spooled string off to a stake or tree and these instruments are available in both feet and meters. In Britain, the chain is no used for practical survey work. However it survives on the railways of the United Kingdom as a location identifier, since railways are entirely linear in topology, the mileage or chainage is sufficient to identify a place uniquely on any given route. Thus a certain bridge may be said to be at 112 mi 63 ch, in the case of the photograph the bridge is near Keynsham, that distance from London Paddington station. On new railway built in the United Kingdom such as High Speed 1
7. Chi (unit) – The chi is a traditional Chinese unit of length. It first appeared during Chinas Shang dynasty approximately 3000 years ago and has since adopted by other East Asian cultures such as Japan, Korea. In its ancient and modern forms, the chi is divided into 10 smaller units known as cun and 10 chi together form one zhang, in the Peoples Republic of China chi has been defined since 1984 as exactly 1/3 of a meter, i. e. 33 1⁄3 cm. However, in the Hong Kong SAR the corresponding unit, pronounced chek in Cantonese, is defined as exactly 0.371475 m, the two units are sometimes referred to in English as Chinese foot and Hong Kong foot. In Taiwan, chi is the same as the Japanese shaku, even earlier, during the Warring States era, the value of chi was essentially the same. It is thought that the ancient Chinese astronomers also used chi as an angular unit, in the 19th century, the value of chi, depending on the part of the country and the application, varied between 31 and 36 cm. In Guangzhou, however, the chi used for local trade varied from 14.625 to 14.81 inches – i. e. very close to the modern chek. The value fixed by a Sino-British treaty for the purposes of customs duties in Hong Kong was 14.1 inches, due to its long history and its widespread usage, chi has also seen metaphorical usages in the Chinese language. For example, chi cun, a made up of the units chi and cun, refers to the dimensions of an object. In informal use, it is sometimes used to refer to the US or imperial foot
8. Cubit – The cubit is an ancient unit based on the forearm length from the middle finger tip to the elbow bottom. Cubits of various lengths were employed in many parts of the world in antiquity, during the Middle Ages, the term is still used in hedge laying, the length of the forearm being frequently used to determine the interval between stakes placed within the hedge. The English word cubit comes from the Latin noun cubitus elbow, from the verb cubo, cubare, cubui, cubitum to lie down, the ancient Egyptian royal cubit is the earliest attested standard measure. Cubit rods were used for the measurement of length, a number of these rods have survived, two are known from the tomb of Maya, the treasurer of the 18th dynasty pharaoh Tutankhamun, in Saqqara, another was found in the tomb of Kha in Thebes. Fourteen such rods, including one double cubit rod, were described and compared by Lepsius in 1865. These cubit rods range from 523.5 to 529.2 mm in length, and are divided into seven palms, each palm is divided into four fingers and the fingers are further subdivided. Use of the royal cubit is also known from Old Kingdom architecture, in 1916, during the last years of the Ottoman Empire and in the middle of World War I, the German assyriologist Eckhard Unger found a copper-alloy bar while excavating at Nippur. The bar dates from c.2650 BC and Unger claimed it was used as a measurement standard and this irregularly formed and irregularly marked graduated rule supposedly defined the Sumerian cubit as about 518.6 mm. The Near Eastern or Biblical cubit is usually estimated as approximately 457.2 mm, in ancient Greek units of measurement, the standard forearm cubit measured approximately 0.46 m. The short forearm cubit, from the wrist to the elbow, in ancient Rome, according to Vitruvius, a cubit was equal to 1 1⁄2 Roman feet or 6 palm widths. Other measurements based on the length of the forearm include some lengths of ell, the Chinese chi, the Japanese shaku, the Indian hasta, the Thai sok, the Tamil, the Telugu, a cubit arm in heraldry may be dexter or sinister. It may be vested and may be shown in positions, most commonly erect. It is most often used erect as a crest, for example by the families of Poyntz of Iron Acton, Rolle of Stevenstone, the Encyclopaedia of Ancient Egyptian Architecture. The Cubit, A History and Measurement Commentary, Journal of Anthropology doi,10. 1155/2014/489757,2014 Media related to Cubit arms at Wikimedia Commons The dictionary definition of cubit at Wiktionary
9. Cun (unit) – The cun, often glossed as the Chinese inch, is a traditional Chinese unit of length. Its traditional measure is the width of a thumb at the knuckle. In this sense it continues to be used to chart acupuncture points on the body in various uses of traditional Chinese medicine. The cun was part of a system, and represented one-tenth of a chi. In time the lengths were standardized, although to different values in different jurisdictions, in Hong Kong, using the traditional standard, it measures ~3.715 cm and is written tsun. In the twentieth century in the Republic of China, the lengths were standardized to fit with the metric system, in Japan, the corresponding unit, sun, was standardized at 1000⁄33 mm. shaku Cun measurements
10. Digit (unit) – The digit or finger is an ancient and obsolete non-SI unit of measurement of length. It was originally based on the breadth of a human finger and it was a fundamental unit of length in the Ancient Egyptian, Mesopotamian, Hebrew, Ancient Greek and Roman systems of measurement. In astronomy a digit is one twelfth of the diameter of the sun or the moon, the digit, also called a finger or fingerbreadth, is a unit of measurement originally based on the breadth of a human finger. In Ancient Egypt it was the unit of subdivision of the cubit. On surviving Ancient Egyptian cubit-rods, the royal cubit is divided into seven palms of four digits or fingers each, the royal cubit measured approximately 525 mm, so the length of the ancient Egyptian digit was about 19 mm. In the classical Akkadian Empire system instituted in about 2150 BC during the reign of Naram-Sin, the cubit was equivalent to approximately 497 mm, so the finger was equal to about 17 mm. Basic length was used in architecture and field division, a digit, when used as a unit of length, is usually a sixteenth of a foot or 3/4. The width of a human male finger tip is indeed about 2 centimetres. In English this unit has mostly fallen out of use, as do others based on the arm, finger, palm, hand, shaftment, span, cubit. It is in equal to the foot-nail, although the term nail can also be used as 1/16 of yard. In astronomy a digit is, or was until recently, one twelfth of the diameter of the sun or the moon and this is found in the Moralia of Plutarch, XII,23, but the definition as exactly one twelfth of the diameter may be due to Ptolemy. Sosigenes of Alexandria had observed in the 1st century AD that on a dioptra, the unit was used in Arab or Islamic astronomical works such as those of Ṣadr al‐Sharīʿa al‐Thānī, where it is called Arabic, إصبعا iṣba, digit or finger. The astronomical digit was in use in Britain for centuries, the unit is apparently not in current use, but is found in recent dictionaries. A finger of a beverage is colloquially referred to as a digit
11. Earth radius – Earth radius is the distance from the Earths center to its surface, about 6,371 km. This length is used as a unit of distance, especially in astronomy and geology. This article deals primarily with spherical and ellipsoidal models of the Earth, see Figure of the Earth for a more complete discussion of the models. The Earth is only approximately spherical, so no single value serves as its natural radius, distances from points on the surface to the center range from 6,353 km to 6,384 km. Several different ways of modeling the Earth as a sphere each yield a mean radius of 6,371 km. It can also mean some kind of average of such distances, Aristotle, writing in On the Heavens around 350 BC, reports that the mathematicians guess the circumference of the Earth to be 400,000 stadia. Due to uncertainty about which stadion variant Aristotle meant, scholars have interpreted Aristotles figure to be anywhere from highly accurate to almost double the true value, the first known scientific measurement and calculation of the radius of the Earth was performed by Eratosthenes about 240 BC. Estimates of the accuracy of Eratosthenes’s measurement range from within 0. 5% to within 17%, as with Aristotles report, uncertainty in the accuracy of his measurement is due to modern uncertainty over which stadion definition he used. Earths rotation, internal density variations, and external tidal forces cause its shape to deviate systematically from a perfect sphere, local topography increases the variance, resulting in a surface of profound complexity. Our descriptions of the Earths surface must be simpler than reality in order to be tractable, hence, we create models to approximate characteristics of the Earths surface, generally relying on the simplest model that suits the need. Each of the models in use involve some notion of the geometric radius. Strictly speaking, spheres are the solids to have radii. In the case of the geoid and ellipsoids, the distance from any point on the model to the specified center is called a radius of the Earth or the radius of the Earth at that point. It is also common to refer to any mean radius of a model as the radius of the earth. When considering the Earths real surface, on the hand, it is uncommon to refer to a radius. Rather, elevation above or below sea level is useful, regardless of the model, any radius falls between the polar minimum of about 6,357 km and the equatorial maximum of about 6,378 km. Hence, the Earth deviates from a sphere by only a third of a percent. While specific values differ, the concepts in this article generalize to any major planet
12. Ell – In English-speaking countries, these included the Flemish ell, English ell and French ell, some of which are thought to derive from a double ell. In England, the ell was usually 45 in, or a yard and it was mainly used in the tailoring business but is now obsolete. Although the exact length was never defined in English law, standards were kept, the Viking ell was the measure from the elbow to the tip of the middle finger, about 18 inches. The Viking ell or primitive ell was used in Iceland up to the 13th century, by the 13th century, a law set the stika as equal to 2 ells which was the English ell of the time. An ell-wand or ellwand was a rod of length one ell used for official measurement, edward I of England required that every town have one. In Scotland, the Belt of Orion was called the Kings Ellwand, the Scottish ell was standardised in 1661, with the exemplar to be kept in the custody of Edinburgh. It comes from Middle English elle and it was used in the popular expression Gie im an inch, an hell tak an ell. The Ell Shop in Dunkeld, Perth and Kinross, is so called from the 18th century iron ell-stick attached to one corner, once used to measure cloth and other commodities in the adjacent market-place. The shaft of the old 17th century Kincardine Mercat cross stands in the square of Fettercairn, Scottish measures were made obsolete, and English measurements made standard in Scotland, by act of parliament in 1824. The Scottish ell was equivalent to, Scottish measures, 3 1⁄12 feet Metric system,94.1318 cm Imperial system,1.03 international yards,37.1 inches This article incorporates text from Dwellys Gaelic Dictionary. Collins Encyclopedia of Scotland Scottish National Dictionary and Dictionary of the Older Scottish Tongue Weights and Measures, by D. Richard Torrance, SAFHS, Edinburgh,1996, ISBN 1-874722-09-9
13. Em (typography) – An em is a unit in the field of typography, equal to the currently specified point size. For example, one em in a 16-point typeface is 16 points, therefore, this unit is the same for all typefaces at a given point size. Typographic measurements using this unit are frequently expressed in decimal notation or as fractions of 100 or 1000, the name em was originally a reference to the width of the capital M in the typeface and size being used, which was often the same as the point size. In metal type, the point size was equal to the height of the metal body from which the letter rises. In metal type, the size of a letter could not normally exceed the em. In digital type, the em is a grid of arbitrary resolution that is used as the space of a digital font. Imaging systems, whether for screen or for print, work by scaling the em to a specified point size, in digital type, the relationship of the height of particular letters to the em is arbitrarily set by the typeface designer. However, as a rough guideline, an average font might have a cap height of 70% of the em. In modern typefaces, the character M is usually less than one em wide. Because of how digital type works, the em now always means the point size of the font in question, in Cascading Style Sheets, the em unit is the height of the font in nominal points or inches. The actual, physical height of any portion of the font depends on the user-defined DPI setting, current element font-size. To make style rules that only on the default font size, another unit was developed. The rem, or root em, is the font size of the element of the document. Unlike the em, which may be different for each element, the rem is constant throughout the document
14. Foot (unit) – The foot is a unit of length in the imperial and US customary systems of measurement. Since 1959, both units have been defined by international agreement as equivalent to 0.3048 meters exactly, in both systems, the foot comprises 12 inches and three feet compose a yard. Historically the foot was a part of local systems of units, including the Greek, Roman, Chinese, French. It varied in length from country to country, from city to city and its length was usually between 250 mm and 335 mm and was generally, but not always, subdivided into 12 inches or 16 digits. The United States is the industrialized nation that uses the international foot and the survey foot in preference to the meter in its commercial, engineering. The foot is legally recognized in the United Kingdom, road signs must use imperial units, the measurement of altitude in international aviation is one of the few areas where the foot is widely used outside the English-speaking world. The length of the international foot corresponds to a foot with shoe size of 13,14,15.5 or 46. Historically the human body has been used to provide the basis for units of length. The foot of a male is typically about 15. 3% of his height, giving a person of 160 cm a foot of 245 mm. These figures are less than the used in most cities over time. Archeologists believe that the Egyptians, Ancient Indians and Mesopotamians preferred the cubit while the Romans, under the Harappan linear measures, Indus cities during the Bronze Age used a foot of 13.2 inches and a cubit of 20.8 inches. The Egyptian equivalent of the measure of four palms or 16 digits—was known as the djeser and has been reconstructed as about 30 cm. The Greek foot had a length of 1⁄600 of a stadion, one stadion being about 181.2 m, the standard Roman foot was normally about 295.7 mm, but in the provinces, the pes Drusianus was used, with a length of about 334 mm. Originally both the Greeks and the Romans subdivided the foot into 16 digits, but in later years, after the fall of the Roman Empire, some Roman traditions were continued but others fell into disuse. In AD790 Charlemagne attempted to reform the units of measure in his domains and his units of length were based on the toise and in particular the toise de lÉcritoire, the distance between the fingertips of the outstretched arms of a man. The toise has 6 pieds each of 326.6 mm, at the same time, monastic buildings used the Carolingian foot of 340 mm. The procedure for verification of the foot as described in the 16th century by Jacob Koebel in his book Geometrei, the measures of Iron Age Britain are uncertain and proposed reconstructions such as the Megalithic Yard are controversial. Later Welsh legend credited Dyfnwal Moelmud with the establishment of their units, the Belgic or North German foot of 335 mm was introduced to England either by the Belgic Celts during their invasions prior to the Romans or by the Anglo-Saxons in the 5th & 6th century
15. Furlong – A furlong is a measure of distance in imperial units and U. S. customary units equal to one-eighth of a mile, equivalent to 660 feet,220 yards,40 rods, or 10 chains. Using the international definition of the inch as exactly 25.4 millimetres, however, the United States does not uniformly use this conversion ratio. Older ratios are in use for surveying purposes in some states and this variation is too small to have many practical consequences. Five furlongs are about 1.0 kilometre, the name furlong derives from the Old English words furh and lang. Dating back at least to early Anglo-Saxon times, it referred to the length of the furrow in one acre of a ploughed open field. The system of long furrows arose because turning a team of oxen pulling a heavy plough was difficult and this offset the drainage advantages of short furrows and meant furrows were made as long as possible. An acre is an area that is one long and one chain wide. For this reason, the furlong was once called an acres length. The term furlong, or shot, was used to describe a grouping of adjacent strips within an open field. Among the early Anglo-Saxons, the rod was the unit of land measurement. A furlong was forty rods, a four by 40 rods, or four rods by one furlong. At the time, the Saxons used the North German foot, when England changed to the shorter foot in the late 13th century, rods and furlongs remained unchanged, since property boundaries were already defined in rods and furlongs. The only thing changed was the number of feet and yards in a rod or a furlong. The definition of the rod went from 15 old feet to 16 1⁄2 new feet, the furlong went from 600 old feet to 660 new feet, or from 200 old yards to 220 new yards. The acre went from 36,000 old square feet to 43,560 new square feet, the furlong was historically viewed as being equivalent to the Roman stade, which in turn derived from the Greek system. In the Roman system, there were 625 feet to the stadium, eight stadia to the mile, a league was considered to be the distance a man could walk in one hour, and the mile consisted of 1,000 passus. After the fall of the Roman Empire, medieval Europe continued with the Roman system, around the year 1300, by royal decree England standardized a long list of measures. Among the important units of distance and length at the time were the foot, yard, rod, furlong, and the mile
16. Gunter's chain – Gunters chain or the surveyors chain is a distance measuring device used for land survey. Gunter used an actual measuring chain of 100 links and these, the chain and the link, have become units of their own. The 66-foot 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 7.92 inches long. Gunters chain reconciled two seemingly incompatible systems, the traditional English land measurements, based on the number 4, the surveyor is assisted by a chainman. A ranging rod is placed in the ground at the destination point. A pin is put in the ground at the end of the chain, and the chain is moved forward so that its hind end is at that point. The whole process is repeated for all the pairs of points required. The process is surprisingly accurate and requires 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, although Gunters chain was later superseded by the steel tape, its legacy was a new unit of length called the chain, which measured 66 feet. This unit still exists as a location identifier on British railways, in the United States, for example, Public Lands Survey plats are published in the chain unit to maintain the consistency of a two-hundred-year-old database. Minor roads surveyed in Australia and new Zealand were in the 19th, in some places other lengths have been used, for example 8.928 inches in Scotland and 10.08 inches in Ireland. The length of a pitch is exactly one chain. A similar American system, of lesser popularity, is Ramsden’s or the engineer’s system, the original of such chains was that constructed, to very high precision, for the measurement of the baselines of the Anglo-French Survey 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 length, each rod consists of 100 links, which are called seconds, ten of which make a prime. Vincent Wing made chains with 9. 90-inch links, most commonly as 33-foot half-chains of 40 links and these chains were sometimes used in the American colonies, particularly Pennsylvania. Distance measurement How to make a Gunters Chain Image from 1675 Nineteenth century image