03-27-2016, 09:16 PM
Get a 1st surface mirror, no ripples, no freezing, (well except for you). Remember to level it. $20 for a 6 X 6 1/4 thick glass unit from www.firstsurfacemirror.com It is more accurate to measure limb on limb. Try UL in morning letting the sun rise up to the AH reflection and subtract semi-diameter. In the PM LL let the sun fall into the AH reflection and add semi-diameter.