Many years ago, I used to build myself a magnetic coil, in order to manually degauss my CRT screens. First I would approach the coil nearest to the center of the screen, then moving it slowly away, while turning the coil on itself. I worked very well
My giant Iiyama Vision Master Pro 17" had a built-in degauss function that looked like a demoscene effect: vertical, shimmering rainbow sine waves.
Sony Trinitrons had that too; on the bigger ones it fired that every startup. CLONKwhiine*