When connecting to a projector, the default setting is to extend your desktop to the projector. This extended display basically creates one big desktop that is split across the two displays. Having one desktop split across two displays can be helpful - when presenting Powerpoint and Keynote both offer presenter displays that preview the next slide and other information. Sometimes you may want to project something while having the ability to work on something else on your computer's standard display. But, you may also want to have the exact same image mirrored on both displays. Follow these instructions to mirror your desktop to the projector.