And the history of "True Meridian", as our laws in USA read.
Nate
Yes very interesting.
My experience is aviators call it magnetic variation and Surveyors call it magnetic declination. In aviation deviation is the variation of the needle caused by being mounted in a metal airplane with electric currents. It is adjusted in the whiskey compass but never perfectly and it varies by heading of the airplane. It is usually adjusted to zero at a magnetic north heading then a card is placed in a holder on the compass which notes the deviation every 30 degrees around the horizon.
We sailors know that process of adjustment as "swinging the compass".
Yep that's what it's called in aviation too.
Port wing, starboard wing, fore and aft.
The collectors and historians of instruments should check the nAmes in 3he acknowledgements.