An interesting article on the pros and cons of the RAF approach and the USAF approach to bombing. The Norden bomb sight was quite accurate at 1500' and lower, but as would be expected rose considerably with increased altitude.
The Allied Rift on Strategic Bombing | Air & Space Forces Magazine (airandspaceforces.com)
On average, in 1939, only a third of the bombs hit within five miles of the aiming point. In the Ruhr Valley—Germany’s industrial heartland, defended by guns and fighters—strikes were even less accurate.
“ In 1943, rather than dropping bombs into pickle barrels, 8th Air Force bombardiers were having trouble hitting the broad side of a barn,” said historian Stephen L. McFarland of Air University. Average CEP soared to 1,200 feet.