Just wondering if we should be factoring in latitude with the earth curvature calculator? For example, if Chicago is at 41.9 degrees, then doesn't that make the earth's E/W circumference 18,581 miles and its radius 2957 miles? I'm probably wrong but, if not, then using the Nowicki photograph, for example - 53 miles distance, 230 feet elevation - that gives 16.05 miles to the horizon rather than 18.57 miles, and - I think - an obscured amount of 1223 feet rather than 793 feet. That seems quite a big difference. Can somebody check please? Cheers.