on a long stage of a nav, Hay to Echuka, i was constantly about 5 miles off course at every 15 min check, i thought i had stuffed up the wind calcs, or the actual wind was much stronger, once on the ground at echuka, there was no wind at all, yet my inflight calcs suggested i had about 20 to 25 kts crosswind..
it wasnt until i departed for shepperton that i realised i had my gps on the shroud next to the compass. made a considerable difference..