I know darkmouse because I have it first hand from the Sim's coders. And many will be flying COD navigating by Heading Time and Airspeed. Variation in 1940 in this part of the Uk was 10 degrees West (the 10W isogonal going pretty much straight through central London) with a mean annual drift of 10.5 seconds Easterly and thats a pretty significant value. On another point any pilot worth his salt can fly a heading +-1degree most real ones do every single day they go to work