What is Unit of measurement?
[[File:CubeLitre.svg|thumb|This cube can hold one [[litre]] of a [[liquid]]]] [[File:Masskrug.jpg|thumb|Beer mugs, at [[Oktoberfest]]: They hold one litre of beer]] '''Units of measurement''' give ''[[standard]]s'' so that the numbers from our measurements refer to the same thing. [[Measurement]] is a process that uses [[number]]s to describe a [[physical quantity]]. We can measure how big things are, how warm they are, how heavy they are, and many other features. For example, the [[metre]] is a standard unit to measure [[length]]. Before 1982, one meter was defined as the distance between two markers on a special metal rod. During that time, saying that something had a length of two meters meant that it was exactly twice as long as the rod used to define the meter. Now scientists define the meter by using the [[speed of light]]. In the past, different units were used in different countries. Today, most units of measure fall into one of three [[System of measurement|systems]]: The older two, the [[Imperial units|British imperial system]] and the closely related [[United States customary units|US customary system]] use the [[Foot (unit of length)|foot]] as a measure of length, the [[Pound (mass)|pound]] as a measure for [[weight]], and the [[second]] as a measure for time. They use other units as well. The number of smaller units that make the bigger units in these two systems varies: For example, there are 12 [[inch]]es in a foot and 16 [[ounce]]s in a pound. The newest and most used of the three systems is the [[metric system]] or [[SI units|SI system]] which use 10, 100 or 1000 of a smaller unit to make a bigger one. For instance, there are 100 centimetres in one metre or 1000 grams in one kilogram. This system uses the metre for length and [[kilogram]] for mass. The common, non-metric measurement of [[time]] does not follow this pattern. The [[second]] is the basis for time measurement, and it is based on the [[sexagesimal]] system: 60 seconds make one [[minute]], and 60 minutes make one [[hour]]. ==