Trigonometry and circles

Something inspired by thoughts on sun dials and a once-held belief that the world was flat; possibly a flat disc floating in water. In essence it may provide (at least) a "holding" answer to an old teenage question: "If zero degrees is north (a.k.a. "up" on a 2D map) for bearings questions, why is it east for more advanced trigonometry?".

The STEM-Ginger Beer Glass answers a separate (but related) question (or begins to).