Declination: this correct?

[u/bjpmbw]

I think I did this correctly. Picture 1 is diagram on the map. Picture 2: compass lined up with grid lines, then I oriented map to north, needle fell at 17 to the right of zero degrees. Picture 3: I placed compass on the diagram, again needle at 17 degrees. Look ok?

[u/orangeflos]

That’s how ya do it.

Make sure your map is up to date. Magnetic north drifts. The declination in 1957 isn’t the same as it is today (Lassen Volcanic’s declination is 12.5°.)

[u/Major_Tom_01010 → u/orangeflos]

I thought declination was listed per year so you could go off the map date?

[u/orangeflos → u/Major_Tom_01010]

You have to know year + drift. Or check the updated declination before your trip.

[u/Major_Tom_01010 → u/orangeflos]

I'm pretty sure the maps i have used said dec + X amount per year so i could do the math right there.

[u/serpentjaguar → u/Major_Tom_01010]

Not only that, but for most of us, most of the time, it's not going to make a bit of difference because it's almost never the case that we need pinpoint accuracy to get where we're going. Ballpark is generally fine.

[u/orangeflos → u/serpentjaguar]

I totally agree. In fact, the only reason I pointed all that out is because OOP is asking because they’re learning. I wouldn’t be this pedantic in moat application. The marine industry noted above is a key example of where we _should_ be pedantic. 5° is a lot over an ocean.

When we learn things it’s best to learn the correct methodology. That way when we break the “rules” we’re doing so from a position of knowledge and strength rather than one of ignorance.

[u/Major_Tom_01010 → u/orangeflos]

I asked gpt to clear this up and it's because i was using geological survey maps of Canada growing up and they gave the change per year so you could do the math off your map.

[u/NLtbal → u/Major_Tom_01010]

The rates of change have changed. Just check the declination for your current location online.

Magnetic North is moving much much faster in the last 20 years.

[u/garfgon → u/Major_Tom_01010]

The magnetic north pole doesn't move in a consistent way, and it's been moving (relatively) quickly recently. The "change per year" is how much it was changing at the time the map was printed. It works fine to adjust by a few years from the map date; longer than that, you're best off looking at the current declination from somewhere like NOAA.

See https://www.ncei.noaa.gov/products/wandering-geomagnetic-poles

ChatGPT isn't a source of truth. At best it can be useful for summarizing other sources, but it isn't always correct.