For further information about referents, see pp. 9 - 11 of Mathematics 10.

In Canada, the SI and imperial measurement systems are the two most commonly used, so it is useful to be familiar with both systems. Throughout much of history, standardized measuring tools were not available, so people used body parts and other familiar objects to measure lengths. Body parts and familiar objects are still commonly used to estimate measurements when accuracy is not important or when measuring tools are not available.