DR wrote:
Declination in navigation is actually
something else but I'll let you googgle for it.


I'm not sure that's really true. In aviation we talk about variation,
but when I'm using 7.5' topo maps on the ground, declination is the term
used for the difference
between magnetic and true north. (See the bottom left of a US DOI
Geologic Survey 7.5' topo.)
Variation and declination are defined the same
If there's a more sophisticated use of the word declination in
navigation, I'm willing to be enlightened.