I can shoot a sight of Polaris on my sextant and calculate my latitude, and I can do this anytime Polaris is visible. Now by shooting Polaris one is measuring the angle between the observer, and the center of the "northern star wheel". That's all well and good because now we have an angle, and the angle decreases as one travels north. Now on the flat earth map this makes perfect sense, because if one travels north from any point, one is moving toward the North Pole, which terrestrially corresponds with the celestial center of the northern star wheel, and all is well. Unfortunately the sky in the Southern Hemisphere has a celestial center that is every bit as centered and as measurable as the one in the northern hemisphere, and if I measure that angle I am again given my latitude, exactly as I am in the north. In FE there is no center to the Southern Hemisphere that could give a correct latitude shot and yet this is easily accomplished by any decent navigator with a sextant, and I have personally done this as well. On a flat earth there could be only one center that would give a correct latitude by measuring it, while a round rotating planet has two, just as we observe. Spinning wheels and clockwork arms are inelegant, and perhaps that could be a forgiven quirk of some creator, but the mathematical impossibility of having two points to measure latitude from on a flat earth is inescapable.