There are three Norths commonly in use in Great Britain. Grid North the direction of a grid line which is parallel to the central meridian on the National Grid. True North is the direction of a meridian of longitude which converges on the North Pole. Magnetic North is the direction indicated by a magnetic compass. Magnetic North moves slowly with a variable rate and currently is west of Grid North in Great Britain The true north is the point in the northern hemisphere about which the plant rotates. Also known as the north pole. Most aircraft in the world now use global positioning systems which are referenced to global co-ordinates and are highly accurate. The thing to realise is the earths magnetism field varies each year be a small amount when referenced to true north. All professional pilots need to understand what is called variation since every aircraft has a magnetic compass in the cockpit should all other systems fail.(Highly, highly UNLIKELY.) Your loft position is referenced to the global navigation position system and this is constant regardless of planetary magnetic variation. Above is small sample of commercial pilot training. Now, how to get my birds to understand all this............... cheers