Monitors control panel
The Monitors control panel in classic Mac OS lets you change the settings for any of the displays connected to the computer.
It can handle resolution, color depth, and ColorSync profiles. Some internal and Apple-branded displays also have brightness, contrast, sound, and geometry settings controls in this control panel.
Video mirroring and/or Video spanning options are available if you have two or more displays connected and your video card(s) support these features.