>I know FS provides it through the "MAGNETIC VARIATION">variable, but this is valid at the aircraft position only. If>you calculate the headings for a flight plan, you need to have>the mag var value anywhere in the world. Any clue?>>EricI would not be surpriced if there would be a formula for it.After all. The difference between both is called the varation and is zero when both poles Magnetic and True are in line with each other from your position. Basically the variation changes because of 2 reasons.The first change is caused by the magnetic field that moves. Maps have to be updated every year or so. The second change is caused by moving your position on the globe. The sum total of the two is your variation.Roelof

I don't think there is a formula for it. I am a private pilot, and I use VFR maps to fly. If you look at the curve that shows the 2

You only have the mag var at the aircraft location, but for following the course you need this variation, not more. The mag var at the waypoint isn't needed for flying.

Hello Arne,You're perfectly right: the mag var at the aircraft location is enough to fly the aircraft correctly along the flight plan.The problem is that for my FMC, I may need to calculate and display the heading between waypoint A and waypoint B, even if A and B are very far from my aircraft. This is why I would like to get the mag var at the location of waypoint A, but I'm afraid it's impossible...Eric

You could cheat a bit and right a nice "T" (true heading) to the course/heading which is used for user defined Waypoints in FMCs. AFAIK only the predefined waypoints have magnetic headings. In a C gauge you might find the magvar in the flightplan file, but I'm not sure.

I was wondering if you got this to work. Also, could a gauge written in C++ do the same thing? I want to have an F16 dive into an unusual attitude when it hits a certain longitude to simulate an auto-evasion of a surface-to-air-missile. Thanks for any help.