According to Wikipedia, the 'Metre' was previously defined as follows:
"The other approach suggested defining the metre as one ten-millionth of the length of the Earth's meridian along a quadrant; that is, the distance from the Equator to the North Pole."If we approximate the Earth as a perfect Circle, then according to the definition above, the Circumference (C) of the Earth would be 4 times 10 Million meters i.e.
C = 40 Million meters.
|Circumference C and Radius R of a circle|
Solving for R = 0.5 * C / Pi, we get the Earth's radius of roughly 6370 kilometers, which is not far from the more accurate 6371 Km value.