Editing Measurement (section)

=== Length ===
{{Main|Length measurement}}
{{See also|List of length, distance, or range measuring devices}}
[[File:CarpentersRule.png|thumb|right|A two-metre carpenter's [[ruler]]]]

A [[ruler]] or rule is a tool used in, for example, [[geometry]], [[technical drawing]], engineering, and carpentry, to measure lengths or distances or to draw straight lines.  Strictly speaking, the ''ruler'' is the instrument used to '''rule''' straight lines and the calibrated instrument used for determining length is called a ''measure'', however common usage calls both instruments ''rulers'' and the special name ''straightedge'' is used for an unmarked rule.  The use of the word ''measure'', in the sense of a measuring instrument, only survives in the phrase ''tape measure'', an instrument that can be used to measure but cannot be used to draw straight lines.  As can be seen in the photographs on this page, a two-metre carpenter's rule can be folded down to a length of only 20 centimetres, to easily fit in a pocket, and a five-metre-long tape measure easily retracts to fit within a small housing.