Principal system of a few nations, the only major industrial one being the
United States. The English system actually consists of two related systems-the
U.S. Customary System, used in the United States and dependencies, and the British
Imperial System. Great Britain, the originator of the latter system, is now
gradually converting to the Metric System. The names of the units and the relationships between them are generally the
same in both systems, but the sizes of the units differ, sometimes
considerably. The basic unit of length is the yard (yd); the basic unit of mass (Weight) is the Pound (lb). Within the English units of measurement there are three different
systems of weights (avoirdupois, troy, and apothecaries'), of which the most widely
used is the avoirdupois. The troy system (named for Troyes, France, where it is
said to have originated) is used only for precious Metals. Apothecaries' weights are based on troy weights; in addition to the pound,
ounce, and grain-which are equal to the troy units of the same name-other units
are the dram and the scruple. For liquid (see States Of Matter) measure, or liquid capacity, the basic unit is the gallon. The U.S. gallon,
or wine gallon, is 231 cubic inches (cu in.); the British imperial gallon is
the volume of 10 lb of pure Water at 62 degrees Fahrenheit (see Temperature)and is equal to 277.42 cu in. The British units of liquid capacity are thus
about 20% larger than the corresponding American units. The U.S. bushel, or
Winchester bushel, is 2,150.42 cu in. and is about 3% smaller than the British
imperial bushel of 2,219.36 cu in.; a similar difference exists between U.S. and
British subdivisions. The barrel is a unit for measuring the capacity of larger
quantities and has various legal definitions depending on the substance being
measured, the most common value being 105 dry quarts. Since the Mendenhall Order
of 1893, the U.S. yard and pound and all units derived from them have been
defined in terms of the metric units of length and Mass, the meter (m) and the kilogram (kg); since 1959 these values are 1
yd = 0.9144 m and 1 lb = 0.45359237 kg. In the United States, the older definition of
the yard as 3,600/3,937 m is still used for surveying, the corresponding foot
(1,200/3,937 m being known as the survey foot. The English units of measurement
have many drawbacks: the complexity of converting from one unit to another, the
differences between American and British units, the use of the same name for
different units (e.g., ounce for both weight and liquid capacity, quart and pint
for both liquid and dry capacity), and the existence of the three different
systems of weights.