NavList:

A slight rider to my previous statement:

Incidentally, as dip is a function of the square root of the height of the observer above the sea or a cloud bank, the higher you climb, the less precise you need to be about your height. That’s why airships such as the R34 and the Zeppelins could obtain passable observations even though, without regular updates to sea level temperature and pressure, they were never really sure of their exact altitude.

That's for a distant sea horizon.  For a land sea junction only 1.5 miles away dip is almost directly proportional to height, at least up to 640 ft.  DaveP