From an older Apple support article titled “Earth‘s Magnetic Field Affects Performance” (via Michael Tsai);
Monitors based on cathode-ray tube (CRT) technology, including those found in iMac computers, use precisely controlled magnetic fields to direct the flow of electrons to the red, green, and blue light emitting phosphors on the monitor. The earth’s magnetic field varies in intensity throughout the world, which can affect the path of this electron beam. During manufacturing, CRT-based monitors are aligned in special areas called helmholtz cages that simulate the magnetic field the monitor is being aligned for. Monitors are typically aligned for the Northern Hemisphere or the Southern Hemisphere, and sometimes for the equatorial region.
A CRT-based monitor purchased in the Northern Hemisphere may not perform correctly if it is moved to the Southern Hemisphere. The reverse is also true because the earth’s magnetic fields are not the same in each hemisphere.
I had no idea this was the case. I have no reason to post this, other than it’s one of the most interesting things I’ve read all week. I couldn’t find any photos of a helmholtz cage as used for manufacturing a CRT display, but they look pretty wild.