Double-line graph

A Double line graph is a line graph with two lines. It has a row of numbers on two sides, showing the intervals, i.e. time, population, concentration of a substence. This is so it can be used to show the change and the rate of change, and the difference between the rates of change of two or more dynamic phenomenon.

Rarely one will see a row of numers on the third side. This means there's a the third line on the graph which represents a phenomenon that cannot be measured with the same units. The phenomemona are related, but they are really different topics. Take, for instance, a graph which shows the growth of the human population over the last two hunderend years on one line, and the second line showing the population of the United States over the same amount of time. A third line would represent the GDO of the US. Because GDO is measured in different units than poputlation, you need to use the third side of the graph. This would might only come half way up the graph, that way