The imperial system of unitsimperial system or imperial units also known as British Imperial [1] or Exchequer Standards of is the system of units first defined in the British Weights and Measures Act and continued to be developed through a series of Weights and Measures Acts and amendments.
The imperial system developed from earlier Hem och Hushåll units as did the related but differing system of customary units of the United States. The imperial units replaced the Winchester Standardswhich were in effect from to By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, but imperial units are still used alongside metric units in the United Kingdom and in some other parts of the former empire, notably Canada.
The modern UK legislation defining the imperial system of units is given in the Weights and Measures Act as amended. The Weights and Measures Act of was initially scheduled to go into effect on 1 May Apothecaries' units are not mentioned in the acts of and In Scotland, apothecaries' units were unofficially regulated by the Edinburgh College of Physicians.
The three colleges published, at infrequent intervals, pharmacopoeiasthe London and Dublin editions having the force of law. Imperial apothecaries' measures, based on the imperial pint of 20 fluid ounces, were introduced by the publication of the London Pharmacopoeia of[8] [9] the Edinburgh Pharmacopoeia of[10] and the Dublin Pharmacopoeia of Metric equivalents in this article usually assume the latest official definition.
Before this date, the most precise measurement of the imperial Standard Yard was 0. Abbreviation of "thousandth of an inch". Also known as mil. The Weights and Measures Act invalidated the various different gallons in use in the British Empire, declaring them to be replaced by the statute gallon which became known as the imperial gallona unit close in volume to the ale gallon.
The Act defined as the volume of a gallon to be that of 10 pounds 4. These measurements were in use fromwhen the new imperial gallon was defined. For pharmaceutical purposes, they were replaced by the metric system in the United Kingdom on 1 January The distinction between mass and weight is not always clearly drawn.
Strictly a pound is a unit of mass, but it is commonly referred to as a weight. When a distinction is necessary, the term pound-force may refer to a unit of force rather than mass. The troy pound The Act of Parliament defined the yard and pound by reference to the prototype standards, and it also defined the values of certain physical constantsto make provision for re-creation of the standards if they were to be damaged.
For the yard, the length of a pendulum beating seconds at the latitude of Greenwich at Mean Sea Level in vacuo was defined as For the pound, the mass of a cubic inch of distilled water at an imperial vikt pressure of 30 inches of mercury and a temperature of 62° Fahrenheit was defined as Since the Weights and Measures ActBritish law defines base imperial units in terms of their metric equivalent.