Why do they work?

Im confused by the section "Why does an analemmatic sundial work?"
How do I find R radius of the suns motion? What happens if I dont make the ellipse with equation 21 and mark it with equation 22?
How tall should the pointer be? Why is 3pm now given by http://plus.maths.org/MI/26154f8cafc9d116bca498bc09cb0f82/images/img-001...?


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