![](https://cos-cdn.shuashuati.com/pipixue-web/2020-1231-2005-12/ti_inject-812ce.png)
When plotted on a graph, cost functions are usually displayed by having the level of activity (machine hours, etc.) plotted on the vertical axis (called the y-axis ) and the amount of total costs corresponding to (or dependent on) the levels of that activity on the horizontal axis (called the x-axis).