Art, KB9MZ wrote:
"Horizontal distance calculated from

S = 1.42 root H----."

The 1.42 is rounded from 1.414 which is the square root of 2. The
formula previously given is:

Miles to the horizon = sq rt 2H

H is in feet.

You can remove 2 from under the radical by expressing it as 1.414. That
is all the RSGB did. I think it is easer to leave the 2 under the
radical, that is just to take the square root of 2x the antenna height
in feet when you are estimating the distance to the horizon in miles.
Usually you can do this in an instant in your head. The results are most
often good enough.

Best regards, Richard Harrison, KB5WZI