curvature of the earth javascript and table

miles inches

ok this is intended to be more accurate,,
here are the numbers i am trying to put in:
earth equator radius 3963.1676 miles,
convert 3963.1676 miles to 251106299.136 inches,
compare a 63360 inches mile line with a 63360 inches mile arc starting at the same point (12 o'clock),
and strike an arc in a clockwise manner and at the clockwise ENDPOINT of the arc draw a line to the closest ENDPOINT of the mile line,
the line which connects the endpoints is 7.99360591 inches in length not quite 8 inches

i use AutoCAD to LENGTHEN the arc using TOTAL to one mile so that AutoCAD sees the arc length not the chord,