Before revision: The individual rectangles that make up the system each measure 1 degree of longitude by 0.5 degrees of latitude and are intended to be roughly square in real world use (approximately 30 nautical miles by 30 nautical miles at temperate latitudes ) although the actual width varies with latitude.
After revision: The individual rectangles that make up the system each measure 1 degree of longitude by 0.5 degrees of latitude and are intended to be roughly square in real world use (approximately 30 nautical miles by 30 nautical miles at 60°N ) although the actual width varies with latitude.