1.1.1 The horizontal and vertical axes
The total costs depend on the output, so the output is the ‘independent variable’ and the total costs are the ‘dependent variable’. When there is a dependence of this kind, the independent variable is plotted on the horizontal axis, which is also called the x axis. In the graph, output has been plotted on the horizontal axis. The dependent variable is plotted on the vertical axis, also called the y axis. The total costs have been plotted on the vertical axis.