Unit of measurement
The definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to the present.
In trade, weights and measures are often a subject of governmental regulation, to ensure fairness and transparency.
[3] Metrology is the science of developing nationally and internationally accepted units of measurement.
Scientific systems of units are a refinement of the concept of weights and measures historically developed for commercial purposes.
[5] Science, medicine, and engineering often use larger and smaller units of measurement than those used in everyday life.
The judicious selection of the units of measurement can aid researchers in problem solving (see, for example, dimensional analysis).
Primitive societies needed rudimentary measures for many tasks: constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials.
Before the establishment of the decimal metric system in France during the French Revolution in the late 18th century,[6] many units of length were based on parts of the human body.
[7] The earliest known uniform systems of measurement seem to have all been created sometime in the 4th and 3rd millennia BC among the ancient peoples of Mesopotamia, Egypt and the Indus Valley, and perhaps also Elam in Persia as well.
In the Magna Carta of 1215 (The Great Charter) with the seal of King John, put before him by the Barons of England, King John agreed in Clause 35 "There shall be one measure of wine throughout our whole realm, and one measure of ale and one measure of corn—namely, the London quart;—and one width of dyed and russet and hauberk cloths—namely, two ells below the selvage..." As of the 21st century, the International System is predominantly used in the world.
After this treaty was signed, a General Conference of Weights and Measures (CGPM) was established.
The CGPM produced the current SI, which was adopted in 1954 at the 10th Conference of Weights and Measures.
One way to make large numbers or small fractions easier to read, is to use unit prefixes.
As science progressed, a need arose to relate the measurement systems of different quantities, like length and weight and volume.
Historically many of the systems of measurement which had been in use were to some extent based on the dimensions of the human body.
These may include the solar mass (2×1030 kg), the megaton (the energy released by detonating one million tons of trinitrotoluene, TNT) and the electronvolt.
[citation needed] In informal settings, a quantity may be described as multiples of that of a familiar entity, which can be easier to contextualize than a value in a formal unit system.
The propensity for certain concepts to be used frequently can give rise to loosely defined "systems" of units.
One example of the importance of agreed units is the failure of the NASA Mars Climate Orbiter, which was accidentally destroyed on a mission to Mars in September 1999 (instead of entering orbit) due to miscommunications about the value of forces: different computer programs used different units of measurement (newton versus pound force).
[20][21] On 15 April 1999, Korean Air cargo flight 6316 from Shanghai to Seoul was lost due to the crew confusing tower instructions (in metres) and altimeter readings (in feet).
[22][23] In 1983, a Boeing 767 (which thanks to its pilot's gliding skills landed safely and became known as the Gimli Glider) ran out of fuel in mid-flight because of two mistakes in figuring the fuel supply of Air Canada's first aircraft to use metric measurements.
