I hesitate to question you, but on my boat "deviation" is the effect on the compass caused by items aboard my boat, and which I can do something about to reduce. "Variation" is dependent on the difference between True North, and Magnetic North, which I just have to accept and apply.
You're probably right - I never worry about the terminology in this area as long as I know the effects! If I were writing a thesis or paper, I'd take care to get it right.
A very grudging response from you. I would have thought that the difference between Variation and Deviation was absolutely vital in precise navigation.
Weren't you taught - True Virgins Make Dull Company?
It's because I have rarely had to use them professionally, so I have to think which is which. I'm the same about left and right - they aren't automatic for me. Magnetic compasses have never been of much professional significance to me; working near the pole they aren't very useful (variation tends to be very large and the restoring force on the needle small, so they are slow to settle and not very accurate, especially if there is a lot of ionospheric activity as there often is in the polar regions). And it happens that my boat's system automatically applies both deviation and variation to the fluxgate compass, so I get true bearings from it. Also, I'm in a location where variation is close to 0; certainly far less than errors in reading a compass. Of course, I can apply them correctly if I need to, but that happens less than once a year; I'm mostly in pilotage waters so I rarely steer a compass course.
I hope he wasn't flying across Antarctica - the ONC and JNC charts of Antarctica are up there with chocolate teapots!
