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Systems of measure either define mass and derive a force unit or define a base force and derive a mass unit [1] (cf. poundal, a derived unit of force in a mass-based system). A slug is defined as a mass that is accelerated by 1 ft/s 2 when a net force of one pound (lbf) is exerted on it.
See Weight for detail of mass/weight distinction and conversion. Avoirdupois is a system of mass based on a pound of 16 ounces, while Troy weight is the system of mass where 12 troy ounces equals one troy pound. The symbol g 0 is used to denote standard gravity in order to avoid confusion with the (upright) g symbol for gram.
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.
Definitions are marked in bold; Unit name Imperial measures US fluid measures US dry measures Metric measures fluid ounces Imperial fluid ounce (fl oz) ≡ 1 imp fl oz. ≈ 0.960 759 940 40 US fl oz ≈ 0.947 102 083 33 US fl oz (food) ≡ 28.413 0625 mL ≡ 0.028 413 0625 L. US fluid ounce (customary) (fl oz) ≈ 1.040 842 730 79 imp fl oz ...
When using "hand in" to convert to hands and inches, the rounded hands and inches values are equivalent, and use the same fraction, if any. Special rounding of the inches value only occurs when "hand in" is the output. For example, if the output is "in hand", the inches value is rounded independently from the hands value.
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.
The troy ounce is the only unit of the system in current use; it is used for precious metals. Although the troy ounce is larger than its avoirdupois equivalent, the pound is smaller. The obsolete troy pound was divided into 12 ounces, rather than the 16 ounces per pound of the avoirdupois system.
In 1959, by international agreement, the definitions of the pound and ounce became standardized in countries which use the pound as a unit of mass. [3] The International Avoirdupois Pound was then created. It is the everyday system of weights used in the United States.