Well since no one's said it, and at the risk of outdated PCness, I'll repeat the jingles I learned back in Power Squadron and around the docks:
To get from From True to the Compass course to steer, you add Westerly error and subtract Easterly error. So, it's True, + - Variation = Magnetic, which + - Deviation =
Compass (and you add Westerly error and subtract easterly error for both variation and deviation, so in shorthand it's:
"TVMDC--Add W", (meaning True, Variation, Magnetic, Deviation, Compass, and add Westerly errors)
How to remember?? as the old non-PC sailors said,
"True Virgins Make Dull Companions--Add Whiskey"
And to go the opposite way, from Compass to True, it's ("CDMVT, Add E") or the jingle"
"Can Dead Men Vote Twice--At Elections?" (here in Louisiana, of course the answer is yes, ha ha)
There may be a more modern set of jingles, but True Virgins and Dead Men is what I grew up with, and I can remember the jingles when I can't remember the formulas.
That's a good way to remember it I guess! It would probably help me if I had an actual chart in front of me. The ones I have are TVA charts for Kentucky and Barkley lakes. No Roses!