Ah but it also depends on your interests, for some reason most suggest latrine-related things :-D
The 14uV/m here is the constant where the other values are extrapolated.
The real fun is that on a ship, unlike the general mass of earth, has a variable groundplane which changes due to salinity, sea height, deck-wash etc. Those old sparks had so much to contend with, yet single wire or dipole are still well-trusted systems.
Alec