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The pound or pound-mass is a unit of mass used in both the British imperial and United States customary systems of measurement.Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.453 592 37 kilograms, and which is divided into 16 avoirdupois ounces. [1]
See WP:MOSNUM#Unit names and the discussion, and see Pound-foot (torque) and Foot-pound (energy). However, some topics use traditional units that conflict with the above convention. To handle these, Module:Convert/makeunits includes a specials table that adds an "alttype" (alternate type) field to certain whitelisted units.
The avoirdupois weight system is thought to have come into use in England around 1300. [citation needed] It was originally used for weighing wool. In the early 14th century several other specialized weight systems were used, including the weight system of the Hanseatic League with a 16-ounce pound of 7200 grains and an 8-ounce mark.
An ounce-force is 1 ⁄ 16 of a pound-force, or about 0.2780139 newtons. It is defined as the force exerted by a mass of one avoirdupois ounce under standard gravity (at the surface of the earth, its weight). The "ounce" in "ounce-force" is equivalent to an avoirdupois ounce; ounce-force is a measurement of force using avoirdupois ounces.
Units for other physical quantities are derived from this set as needed. In English Engineering Units, the pound-mass and the pound-force are distinct base units, and Newton's Second Law of Motion takes the form = where is the acceleration in ft/s 2 and g c = 32.174 lb·ft/(lbf·s 2).
Troy weight, avoirdupois weight, and apothecaries' weight are all built from the same basic unit, the grain, which is the same in all three systems. However, while each system has some overlap in the names of their units of measure (all have ounces and pounds), the relationship between the grain and these other units within each system varies.
For example, the freezing point of water is 0 °C and 32 °F, and a 5 °C change is the same as a 9 °F change. Thus, to convert from units of Fahrenheit to units of Celsius, one subtracts 32 °F (the offset from the point of reference), divides by 9 °F and multiplies by 5 °C (scales by the ratio of units), and adds 0 °C (the offset from the ...
An imperial fluid ounce is 1 ⁄ 20 of an imperial pint, 1 ⁄ 160 of an imperial gallon, or exactly 28.4130625 mL. A US customary fluid ounce is 1 ⁄ 16 of a US liquid pint, 1 ⁄ 128 of a US gallon, or exactly 29.5735295625 mL, making it about 4.084% larger than the imperial fluid ounce. A US food labeling fluid ounce is exactly 30 mL.