For educational purposes only
History of Measurement
How far away is London? What is your mass? How tall is your best friend? Today, it is possible
to quickly answer all these questions and many more because of precise and universal
standards of measurement. We have standards for measuring length, area, mass, volume,
temperature, and other variables. But centuries ago, there were few agreed-upon standards.
How did they come about?
Very early standards of measurement relied upon the width of the human palm, the length of
the human foot, and the length from the elbow to the tip of the middle finger, which was called
the cubit. Even today you can see people use these measurements as a quick way to determine
distance. The disadvantage of this, of course, is that such measurements are imprecise. After
all, palms, feet, and forearm length differ from person to person. As early as 3000 B.C.
attempts were made to standardize the cubit. The Egyptian royal cubit came to be a length of
approximately 52.3 cm, whereas the Sumerian was about 49.5 cm. Longer distances were less
precisely defined for several thousand years. For example, the Roman mile was considered to
be the distance covered by 1000 double paces, roughly equal to 1.5 kilometers.
Early measurements of area were also not very precise. An acre came to be defined as the
amount of land that could be plowed by a yoke of oxen in one day. Of course, the area plowed
varied greatly according to the nature of the land and the heartiness of the oxen.
Volume and Mass
For things like grain and liquids, measuring volume was usually easier to do than measuring
mass. It was simpler to fill a container of a specific size with seeds, water, honey, or oil than it
was to weigh these substances. However, highly valuable substances demanded a more precise
system of measurement, and for certain substances, measurements of mass were more
accurate. Measurement of mass was first used for gold dust about 5000 B.C. But the use of the
balance scale did not come about until more than 2000 years later. This kind of scale was made
of a beam that rests on a pivot point at its center and has one pan to hold objects to be
weighed, or massed, and another pan that holds standard masses. The same kind of scale is still
used to make precise measurements of mass today.
The Metric System
The invention of the metric system led to the standardization of measurement through much of
the world. It began as a decimal system of physical units based on a unit of length known as
the meter. This system was adopted by law in France during the 1790s. During these years,
French scientists measured part of the distance from the equator to the North Pole on a line
running through Paris. They then estimated the total distance and divided it into ten-millionths.
In other words, a distance one-quarter around the Earth was made up of ten million meters.
The problem with this was that the calculations of the French scientists were based on the
assumption that Earth was a perfect sphere. When scientists later discovered that Earth was
not a sphere, the meter needed to be based on a different standard. It became defined
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For educational purposes only
internationally as the distance between two lines etched on a bar of platinum-iridium alloy,
which was kept at a constant temperature at Sevres, near Paris.
By the 1980’s, scientists developed a still more precise standard. A meter came to be defined
internationally as the length of the path traveled by light in a vacuum during a time interval of
1 / 299, 792, 458 of a second.
Despite the invention of the metric system, people in the U.S. and Great Britain continued to
use the inch, foot, yard, and mile to measure length. The British yard was based upon a
standard known as the imperial standard yard, which was the distance between two marks on a
bronze bar manufactured in 1839 and then recreated in 1845. But eventually it was discovered
that the bar was shrinking at a rate of one millionth of an inch per year. In 1899, in response to
this problem, the U.S. decided to base its standard of length on a standard meter. In 1960, the
Eleventh Congress on Weights and Measures called for a universal system of measurement
based on the metric system. Six base units of measurement were decided then and one more
was added in 1971. They include the meter, the kilogram, the second, the ampere, and the
kelvin. They also include the mole, which expresses the molecular weight of a substance in
grams, and the candela, which measures light intensity. This international standard became
known as the SI system, which stands for Systeme International. Established units of
measurement with special units, such as the nautical mile, the knot, and the hectare were
temporarily accepted as valid, but these may come up for review in the future. At the
conference a new standard for the meter was established. Henceforth it would be based on
wavelengths of light from a krypton- 86 source.
People in the United States still use inches, feet, miles, pounds, and other common
measurements, but all of these are now legally based on metric standards. Since 1975, the U.S.
has officially committed itself to convert to the metric system. However, efforts among
businesses, governments, and individuals have been slow-moving and many people still feel
more comfortable using the English system.
Which system do you feel more comfortable using?
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