My coworker showed me this trick the other day - simple but effective! I used it to keep an eye on the legibility of a logo I was working on, but it could be useful for anything you're doing while zoomed in. Saves a lot of Ctrl + and Ctrl - ing. ^_^
I was about to say that's exactly like the navigator, 'cept the navigator's a tiny bit bigger and (in my opinion ) better, because if you click on the navigator, it also goes straight to it... but I see someone else has said that already, in a lot less words.
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Thanks for sharing