What is the diameter of the earth? [geography.about.com]
The diameter of the earth at the equator is 7,926.41 miles (12,756.32 kilometers).
But, if you measure the earth through the poles the diameter is a bit shorter - 7,901 miles (12,715.43 km). Thus the earth is a tad wider (25 miles / 41 km) than it is tall, giving it a slight bulge at the equator. This shape is known as an ellipsoid or more properly, geoid (earth-like).
7926.41 / 39.37 = 201.33 BASE OF G3 = 201.42 (+ OR -)
If we add up the two distances we get here we get 7926.41 + 7901.0 = 15827.41 / 2 = 7913.705
And I have my circle at 7915.8082 .. Pretty close I should think.