Every compass ... will suffer from local deviation effects, due to local magnetic interferences ... - almost any ferrous or magnetic object. These effects will vary at different points of the compass, for example only a degree or two at a due north heading, and 5 or 6 degrees at an easterly heading.
No, not the Tom Cruise movie. This is the story of Ronald and Reginald Kray, two British gangsters from the 50s and 60s. I've been interested in them since seeing the film The Krays (staring the brothers from Spandau Ballet) back in the early 90s.