The earliest recorded systems ofweights and measures originate in the 3rd or 4th millennium BC.[1] Even the very earliest civilizations needed measurement for purposes of agriculture, construction and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship tounits of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science ofmetrology. The discovery and application ofelectricity was one factor motivating the development of standardized internationally applicable units.
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The comparison of the dimensions of buildings with the descriptions of contemporary writers is another source of information. An interesting example of this is the comparison of the dimensions of the GreekParthenon with the description given byPlutarch from which a fairly accurate idea of the size of theAttic foot is obtained. Because of the comparative volume of artifacts and documentation, much more is known today about the state-sanctioned measures of large, advanced societies than about those of smaller societies or about the informal measures that often coexisted with official ones. In some cases, there are only plausible theories and different interpretations can be matched to the evidences.
It is possible to group official measurement systems for large societies into historical systems that are relatively stable over time, including: the Babylonian system, the Egyptian system, the Phileterian system of thePtolemaic age, the Olympic system of Greece, the Roman system, theBritish system, and themetric system.
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The earliest known uniform systems of weights and measures seem all to have been created at some time in the4th and3rd millennia BC among the ancient peoples ofEgypt,Mesopotamia and theIndus Valley, and perhaps alsoElam (inIran) as well.
EarlyBabylonian andEgyptian records and theHebrew Bible indicate that length was first measured with the forearm, hand, or finger and that time was measured by the periods of the sun, moon, and other heavenly bodies. When it was necessary to compare the capacities of containers such asgourds orclay or metal vessels, they were filled with plant seeds which were then counted to measure thevolumes. When means for weighing were invented, seeds and stones served as standards. For instance, thecarat, still used as a unit for gems, was derived from thecarob seed.
Before the establishment of the decimalmetric system inFrance during theFrench Revolution in the late18th century,[2] many units of length were based on parts of thehuman body.[3][4] The Nippurcubit was one of the oldest knownunits of length. The oldest known metalstandard forlength corresponds to this Sumerian unit and dates from 2650 BCE.[5][6] Thiscopper bar was discovered inNippur, on the banks of theEuphrates, and is kept in theIstanbul Archaeological Museum. Archaeologists consider that this 51.85 centimetres long unit was the origin of theRoman foot. Indeed, theEgyptians divided theSumerian cubit into 28fingers and 16 of these fingers gave a Roman foot of 29.633 cm.[6][4]
Thegrain was the earliestunit of mass and is the smallest unit in theapothecary,avoirdupois, Tower, andtroy systems. The early unit was a grain of wheat or barleycorn used to weigh the precious metals silver and gold. Larger units preserved in stone standards were developed that were used as both units of mass and of monetary currency. Thepound was derived from themina (unit) used by ancient civilizations. A smaller unit was theshekel, and a larger unit was thetalent. The magnitude of these units varied from place to place. The Babylonians and Sumerians had a system in which there were 60 shekels in a mina and 60 minas in a talent. The Roman talent consisted of 100 libra (pound) which were smaller in magnitude than the mina. The troy pound (~373.2 g) used in England and the United States for monetary purposes, like the Roman pound, was divided into 12 ounces, but the Roman uncia (ounce) was smaller. The carat is a unit for measuring gemstones that had its origin in the carob seed, which later was standardized at 1/144 ounce and then 0.2 gram.
Goods of commerce were originally traded by number or volume. When weighing of goods began, units of mass based on a volume of grain or water were developed. The diverse magnitudes of units having the same name, which still appear today in our dry and liquid measures, could have arisen from the various commodities traded. The larger avoirdupois pound for goods of commerce might have been based on volume of water which has a higherbulk density than grain.
The stone, quarter, hundredweight, and ton were larger units of mass used in Britain. Today only the stone continues in customary use for measuring personal body weight. The present stone is 14 pounds (~6.35 kg), but an earlier unit appears to have been 16 pounds (~7.25 kg). The other units were multiples of 2, 8, and 160 times the stone, or 28, 112, and 2240 pounds (~12.7 kg, 50.8 kg, 1016 kg), respectively. The hundredweight was approximately equal to two talents. The "long ton" is equal to 2240 pounds (1016.047 kg), the "short ton" is equal to 2000 pounds (907.18474 kg), and the tonne (or metric ton) (t) is equal to 1000 kg (or 1 megagram).
The division of the circle into 360 degrees and the day into hours, minutes, and seconds can be traced to the Babylonians who had asexagesimal system of numbers. The 360 degrees may have been related to ayear of 360 days. Many othersystems of measurement divided the day differently—counting hours,decimal time, etc. Othercalendars divided the year differently.
Decimal numbers are an essential part of the metric system, with only one base unit and multiples created on the decimal base, the figures remain the same. This simplifies calculations. Although theIndians used decimal numbers for mathematical computations, it wasSimon Stevin who in 1585 first advocated the use of decimal numbers for everyday purposes in his bookletDe Thiende (old Dutch for 'the tenth'). He also declared that it would only be a matter of time before decimal numbers were used for currencies and measurements.[7]His notation for decimal fractions was clumsy, but this was overcome with the introduction of the decimal point, generally attributed toBartholomaeus Pitiscus who used this notation in his trigonometrical tables (1595).[8]
In 1670,Gabriel Mouton published a proposal that was in essence similar toJohn Wilkins' proposal for a universal measure, except that his base unit of length would have been 1/1000 of aminute of arc (about 1.852 m) of geographical latitude. He proposed calling this unit the virga. Rather than using different names for each unit of length, he proposed a series of names that had prefixes, rather like the prefixes found in SI.[9]
In 1790,Thomas Jefferson submitted areport to theUnited States Congress in which he proposed the adoption of a decimal system of coinage and of weights and measures. He proposed calling his base unit of length a "foot" which he suggested should be either3⁄10 or1⁄3 of the length of a pendulum that had a period of one second—that is3⁄10 or1⁄3 of the "standard" proposed by John Wilkins over a century previously. This would have equated to 11.755 English inches (29.8 cm) or 13.06 English inches (33.1 cm). Like Wilkins, the names that he proposed for multiples and subunits of his base units of measure were the names of units of measure that were in use at the time.[10] The great interest ingeodesy during this era, and the measurement system ideas that developed, influenced how the continental US wassurveyed and parceled. The story of how Jefferson's full vision for the new measurement system came close to displacing theGunter chain and the traditionalacre, but ended up not doing so, is explored inAndro Linklater'sMeasuring America.[11]
Themetric system was first described in 1668 and officially adopted by France in 1799. Over the 19th and 20th centuries, it became the dominant system worldwide, although several countries, including the United States, China, and the United Kingdom continue to use their customary units.[12] Among the numerous customary systems, many have been adapted to become an integer multiple of a related metric unit: TheScandinavian mile is now defined as 10 km, theChinese jin is now defined as 0.5 kg, and theDutch ons is now defined as 100 g.
The UK is the country stuck in the middle of both systems, being the birthplace of the imperial system itself. Here, metric is partially adopted but miles persist, and people routinely refer to pints, miles per gallon, pounds and even stone in their everyday lives.
This article incorporatespublic domain material fromSpecifications, Tolerances, and Other Technical Requirements for Weighing (Handbook 44 -2018).National Institute of Standards and Technology.