Reveal All Possible Screen Resolutions for a Display Connected to a Mac
This works to reveal additional screen resolution choices for any display connected to a modern Mac, it also applies to all modern versions of OS X:
1. Open System Preferences from the Apple menu in OS X
2. Click on “Display”
3. Under the ‘Display’ tab, hold down the OPTION / ALT key while you press on the ‘Scaled’ button alongside Resolution to reveal all available screen resolution options for the display
4. Choose the resolution desired from the complete list of available screen resolutions, then close out of System Preferences as usual
You must hold the Option key when clicking on ‘Scaled’ to reveal all possible screen resolutions for the external display(s), and if you have multiple external displays in use on a Mac, you’ll want to hold the option key when choosing “Scaled” and selecting a resolution for each connected display.
For example, here’s the default selection of “Scaled” resolutions shown on a particularly 24″ external display connected to a MacBook Pro: