When you plug in a second monitor to Macintosh computer, it may display an exact copy or ‘mirror image’ of what is on your first display. This is called mirroring. This is fine if you are doing a presentation and you want to see on your laptop screen exactly what is on the projector, but it’s not very useful at home to have the same thing on both screens. If you’d like to see different things on each screen, so the second screen gives you more desktop space, you need to turn mirroring off. Here’s how.