The formula for Line of Sight is:
distance = Sqrt(2*R*h+(h^2)), where:
R = Radius of the Earth
h = Eye Height
Note: Use the same units for all variables (km, nm, yds, m, etc)
Since the Earth is a Oblate Spheroid (a pear), the diameter and thus the radius varies according to location. The Earth's approximate radius is:
6357 ~ 6378 km
3950 ~ 3963 miles, or 8000067 ~ 8026396 yds (nm = 6076)
Therefore: Using the values in the tables listed in this thread, an Eye Height of 79 ft yields a distance of 20,610 yds.
By the formula, where the Earth's Radius is 8000067 yds and the Eye Height is 26 yds (79/3), the distance to the horizon is 20,527 yds.
That's pretty close!
Old_tex