Originally Posted by
aviationluver
I noticed if you have a long leg, especially of a few hundred miles, the heading at the beginning of the leg and at the end of the leg differ by a few degrees. I'm thinking the difference is due to Magnetic Variation and the curvature of the Earth. Are there any other factors?
True heading will vary continuously along a route, assuming you are flying a Great Circle (unless your route is due north/south). It doesn't have to be a long route - if you overfly, say, Heathrow's east-west runways, your heading will differ at each end by a fraction of a degree.