Hi Spir4,
If the difference in variation was 20 degrees between the VOR and the aircraft, then flying with the needle pointing directly upwards would send you away by 20 degrees initially.
If you wanted to fly a constant QDM, then your heading would have to be 20 degrees away from the needle initially (seen as apparent drift), and as the difference in variation reduced to zero, then you'd finish with the needle pointing directly ahead.
Last edited by rudderrudderrat; 9th Jun 2013 at 16:59.
Reason: tidy up