In my younger days I sailed across a portion of the Pacific Ocean using only a sextant for navigation. Fundamental to finding your way across oceans with no land in sight is the relationship of the sun to the horizon at noon, specifically its angle (altitude). It’s a crazy cool system that works every time. I have a question for you, can you produce a flat earth diagram where two observers measure sun altitudes differing by 10°, yet are always 600 nautical miles apart regardless of where on Earth they are? This is an interesting question because it is not hypothetical. Cheers. 🙂