I am trying to work out what the different distances would be , measured at ground level and at the top, between two perfectly straight, plumb buildings each a kilometer high (like the trade towers were, only taller) . For the sake of argument assume the buildings are one kilometer apart (although I think the difference between the two measurements will be the same no matter what the actual distance apart, within reason)

Obviously the way to calculate it is to use the radius of the earth (6371 kilometers) as each side of an equilateral triangle with the base measuring one kilometer, and then calculate what the base of the triangle would be with each side 6372 kilometers, subtended by the same angle.

I am not expert enough to make use of the Windows 7 calculator to figure this out (although I do have an elementary grasp of trigonometry) , so any assistance on how to use the calculator to do the math would be welcome , as would the actual results of the calculation.

I do appreciate that a perfectly straight, plumb building a kilometer high is an engineering impossibility … it would be built with stepped sides, getting narrower the higher you went , but let’s just pretend .