How to Read a Ruler?

A ruler is nearly always divided into units, then into sub units. To read one, you need to know what unit is measured (usually inches or centimetres, but this can vary). Then you simply count the number of units that are within the distance you want to measure. There are also often sub-units, such as millimetres, that are divisions of the basic unit. You'll need to add them, if the distance .
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