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As civilization developed, so too did the need for units of measurement. These were required for numerous tasks such as: constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials.
Contents
Earliest known systems
The earliest known uniform systems of weights and measures seem all to have been created at some time in the 4th and 3rd millennia BC among the ancient peoples of Egypt, Mesopotamia and the Indus Valley, and perhaps also Elam (in Iran) as well.
The system attributed to the Indus Valley Civilization (ca. 2600 BC) is sometimes cited as particularly accurate. Based on an ivory scale found in Lothal, their smallest unit corresponded to approximately 1.704 mm (0.067 in), which S.A. Rao, writing in 1970, thought was the smallest division ever recorded on a scale of the Bronze Age.
Early Babylonian and Egyptian records and the Hebrew 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 as gourds or clay or metal vessels, they were filled with plant seeds which were then counted to measure the volumes. When means for weighing were invented, seeds and stones served as standards. For instance, the carat, still used as a unit for gems, was derived from the carob seed.
Units of length
The Egyptian cubit, the Indus Valley units of length referred to above and the Mesopotamian cubit were used in the 3rd millennium BC and are the earliest known units used by ancient peoples to measure length. The units of length used in ancient India included the dhanus (bow), the krosa (cry, or cow-call) and the yojana (stage).
The common cubit was the length of the forearm from the elbow to the tip of the middle finger. It was divided into the span of the hand or the length between the tip of little finger to the tip of the thumb (one-half cubit), the palm or width of the hand (one sixth), and the digit or width of the middle finger (one twenty-fourth). The Royal Cubit, which was a standard cubit enhanced by an extra palm—thus 7 palms or 28 digits long—was used in constructing buildings and monuments and in surveying in ancient Egypt. The inch, foot, and yard evolved from these units through a complicated transformation not yet fully understood. Some believe they evolved from cubic measures; others believe they were simple proportions or multiples of the cubit. In whichever case, the Greeks and Romans inherited the foot from the Egyptians. The Roman foot (~296 mm) was divided into both 12 unciae (inches) (~24.7 mm) and 16 digits (~18.5 mm). The Romans also introduced the mille passus (1000 paces) or double steps, the pace being equal to five Roman feet (~1480 mm). The Roman mile of 5000 feet (1480 m) was introduced into England during the occupation. Queen Elizabeth I (reigned from 1558 to 1603) changed, by statute, the mile to 5280 feet (~1609 m) or 8 furlongs, a furlong being 40 rod (unit)s (~201 m) of 5.5 yards (~5.03 m) each.
The introduction of the yard (0.9144 m) as a unit of length came later, but its origin is not definitely known. Some believe the origin was the double cubit, others believe that it originated from cubic measure. Whatever its origin, the early yard was divided by the binary method into 2, 4, 8, and 16 parts called the half-yard, span, finger, and nail. The association of the yard with the "gird" or circumference of a person's waist or with the distance from the tip of the nose to the end of the thumb of King Henry I (reigned 1100–1135) are probably standardizing actions, since several yards were in use in Britain. There were also Rods, Poles and Perches for measurements of length. The following table lists the equivalents.
Length
12 lines = 1 inch
12 inches = 1 foot
3 feet = 1 yard
1760 yards = 1 mile
36 inches = 1 yard
440 yards = quarter-mile
880 yards = half-mile
100 links = 1 chain
10 chains = 1 furlong
8 furlongs = 1 mile
4 inches = 1 hand
22 yards = 1 chain
5.5 yards = 1 rod, pole or perch
4 poles = 1 chain
40 poles = 1 furlong
Typographical units
The use in typography of the point, which was one twelfth of a ligne in the customary French measures of the Ancien Régime, as a unit for measuring print type predates the metric system. Various typographic points were defined, including the Truchet point by Sébastien Truchet (1657–1729), the Fournier point by Pierre Simon Fournier in 1737 and the Didot point by the Didot brothers, Francois Ambroise and Pierre Francois, in 1755 or 1767 or 1783, which was exactly two Truchet points. The point was first used in the United States in 1878 or 1872 by a Chicago type foundry (Marder, Luse, & Co.).
The point was defined as 1/12 of a pica consisting of 1/6 of an inch truncated to thousandths of an inch (1/12 of 0.166 inches) in the USA in 1886 and was quickly adopted by Britain and its colonies;. This number has been approximated in various ways depending on the technology, prejudices, and information available to engineers involved in the production of typesetting machinery since then. Common approximations in use are 1/72.27 inch (now equal to 0.3514598 mm) and simply 1/72 of an inch. Other typographic points are used in other countries.
The pica in any of several related systems measures 12 points.
Units of mass
The grain was the earliest unit of mass and is the smallest unit in the apothecary, avoirdupois, Tower, and troy 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. The pound was derived from the mina used by ancient civilizations. A smaller unit was the shekel, and a larger unit was the talent. 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 higher bulk 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 ton of 2240 pounds is called the "long ton". The "short ton" is equal to 2000 pounds (~907 kg). A tonne (t) is equal to 1000 kg.
Units of time and angle
The division of the circle into 360 degrees and the day into hours, minutes, and seconds can be traced to the Babylonians who had sexagesimal system of numbers. The 360 degrees may have been related to a year of 360 days. Many other systems of measurement divided the day differently -- counting hours, decimal time, etc. Other calendars divided the year differently.
Metric conversion
The metric system was first described in 1668, and officially adopted by France in 1799. Over the course of the 1800s and 1900s, it became the dominant system worldwide including the only measurement system enacted by law by the United States. Numerous countries continue to use their customary units. The American system is unusual, however, in not having adjusted itself to close metric values in the manner of the Scandinavian mile (now 10 km exactly), the Chinese jin (now 0.5 kg exactly) or the Dutch ons (now 100 g).