To check how much of your computer's processor is currently being used, go to the Resources tab and look at the CPU History chart. This tells you how much work the computer is currently doing.

Many computers have more than one processor (sometimes called multi-core systems). Each processor is shown separately on the chart. If you want, you can change the color used for each processor by clicking one of the colored blocks below the chart.

You can also change how rapidly the chart is updated (the update interval), and how the lines for each processor are displayed (e.g. as a stacked area chart). Change the relevant options by clicking System Monitor, then select Preferences, and then the Resources tab.