These methods are set forth and exemplified in **Graphics**, by R.

There are also cases in which **graphics** and mensuration are used jointly; a variable numerical quantity is represented by a graph, and the principles of mensuration are then applied to determine related numerical quantities.

Graphic representation thus rests on the principle that equal numerical quantities may be represented by equal lengths, and that a quantity mA may be represented by a length mL, where A and L are the respective units; and the science of **graphics** rests on the converse property that the quantity represented by pL is pA, i.e.