Here's the Tutorial on How to zoom in on your screen on iMac.
I dont know if this is something everyone knows but I thought it is pretty cool, 1. press the command and option key and the asteris (key 8) (to enable the feature) 2. hold command and option and press +, or - to zoom in and out, according to jorey in MacRumors.
Yes, this is pretty widely known, but still a good tip. Can come in handy. Also, CMD-OPT-CTRL-8 inverts colors. Just don't give yourself a seizure.
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