The units were interrelated. Units of one measure, such as length, increased by powers of ten (millimeters, centimeters, decimeters, meters). A liter was the volume of a cube 10 centimeters on a side.

Units of speed are always a unit of length per unit of time. Different units of length and time may be chosen depending on the situation. This makes it easier to read the measurements. For example ...

When converting between units for an area calculation, remember that a square has two dimensions, the length and the width. Draw two identical squares next to one another. Label one in metres (1 m ...