This is a circular test pattern with total diameter of 200mm.

I designed it to test the bed levelling and adhesion of my Kossel printer. It uses minimal filament and covers the entire 200mm area with a pattern of concentric circles, with more smaller circles embedded in it. It gives a good impression about where any low points in your bed are after going through the arduous manual levelling procedure. The thin lines also give the adhesion of your bed the ultimate test.