When I learned to drive one of HM's war canoes about, magnetic variation and deviation was bread and butter stuff as we still used compasses to get places and to avoid the hard bits (with a bit of help from Messrs Decca and Loran to be fair). Subsequently, in the RAF, when I flew for fun, I followed roads, rivers and railways but occasionally I used a magnetic bearing to find my next waypoint. The variation correction was usually to throw in a tad of right hand down and fix off the ground I as wasn't allowed to fly in clouds. Even as a spotty youth, when I started walking and using bearings I knew the theory but in reality it tended to be same principle, let the needle point a tad west of north and use geography to fix. Nowadays, my compass never comes out and anyway, in the UK, magnetic N and True N are now so close together who cares?