This is the *actual* color wheel for determining complementary colors. Most other wheels are false, for example green and red are not opposite, green and magenta are, and red and cyan. Normal color wheels are thus over-simplified to criminal distortion.
I consider this very important for anybody working with colors in any creative field. You can't understand color harmonies if you have false data about it.
Complentary colors of course are two colors which when mixed gives a neutral white/grey/black. That's simple but strong harmony.
I spoke to the maker of the wheel at RealColorWheel, he said he had developed it through years of work. Which explains why it was so hard to find.