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 average temperature of the planet (over the same amount of time). A third line would represent the percentage of carbon dioxide in the atmosphere. Because carbon dioxide wasn't measured very much two hundered years ago, the line would start at about 1900. Because for percentage you need the third side of the graph, it's less confusing if the line is in the corner. 100% might only come half way up the graph, that way