When I studied surveying, compass declination was a simple thing – there was a page in the text that showed a map of North America, the geographic north pole and the magnetic north pole, and a series of lines showing where to set the declination so you could push a line due north (or south or east or any direction you wanted to go.
Back when (and where) George Washington was surveying, the magnetic north pole was pretty much on a straight line with the geographic north pole. The really precise guys would stay up at night and establish a reference line from Polaris, or you might establish a line on the solstice, but in general, American surveyors had a lot of confidence in the magnetic compass.
Since I retired, I’ve had to change my references – the page on the old blue surveying book that showed how much correction was needed to correct my compass bearing just doesn’t pack it anymore. Magnetic north has moved a long way in my lifetime:
So now, before I decide to push a line out with a compass, I get online. Fortunately, NOAA provides more information than weather: noaa.gov/maps/historical_declination shows the movement of magnetic north from 1500 to present (nobody paid much attention before 1500).
My goto place for updating the declination is ngdc.noaa.gov
If I don’t use the NOAA information, I have a stretch of road that runs east-west where I can adjust declination without needing technology. The more modern folks just use GPS – though most of them are probably more comfortable without a compass than I.
Things change. And that’s OK, so long as I stay current and change with them.
Trego's Mountain Ear 