A ruler or rule is an instrument use in geometry, technical drawing and engineering/building to measure distances and/or to rule straight lines. Strictly speaking, the ruler is essentially a straightedge used to rule lines and the calibrated instrument used for determining measurement is called a 'measure'. However, common usage is that a ruler is a calibrated straightedge that can be used for making measurements.

Trivia about ruler

  • Charles Dickens' Mr. Creakle likes to whack pupils on the hand with this measuring device