My MacBook's external monitor is magnified When I initially got my MacBook, I connected my external monitor and it worked fine. Last night I disconnected it and when I connected them back together, the resolution on the external monitor was changed. The overall display is now magnified (for example as I'm writing this I have to scroll down to see this). 

I tried to change the resolution settings in Preferences but this didn't help to change it back. So how can I set the resolution of the external monitor back to a sane state?
Maybe you accidentally magnified your screen using Universal Access's screen Zoom, it can survive display detects with out zooming back out. And it can be accidentially triggered via holding down the &#8984; key or some customizable key and then scrolling up or down with your mouse or track pad. 


Look in System Preferences under the "Univeral Access" section.  
Once there click on the "Seeing" tab. Is "Zoom:" on? If yes then continue. 
Press &#8984; + &#8997; + - to zoom out.