RAF General Service Practice Test

The observed difference between true north and grid north in the British Isles is typically in the range of 3° to 5° west. This discrepancy arises from the fact that the Earth's magnetic field is not perfectly aligned with the geographical north pole. Instead, maps are often based on a grid system that can differ slightly from true north due to the curvature of the Earth and local variations in geography.

This difference is important for navigation and map reading in the British Isles, as it affects how one interprets directions and bearings. Understanding this distinction ensures accurate navigation, especially when converting between true bearings and grid bearings, which is a fundamental skill for those in military or outdoor activities.

The other options present either lower or higher variations, which do not accurately reflect the typical discrepancy observed in the British Isles. Consequently, the answer that indicates a difference of 3° to 5° west aligns with standard navigational knowledge in that area.