British gunnery control systems, based on Dreyer tables, were well in advance of the German ones, as demonstrated by the proportion of main calibre hits made on the German fleet. Because of its demonstrated advantages, it was installed on ships progressively as the war went on, had been fitted to a majority of British capital ships by May 1916, and had been installed on the main guns of all but two of the Grand Fleet's capital ships. The Royal Navy used centralised fire-control systems on their capital ships, directed from a point high up on the ship where the fall of shells could best be seen, utilising a director sight for both training and elevating the guns. In contrast, the German battlecruisers controlled the fire of turrets using a training-only director, which also did not fire the guns at once. The rest of the German capital ships were without even this innovation. German range-finding equipment was generally superior to the British FT24, as its operators were trained to a higher standard due to the complexity of the Zeiss range finders. Their stereoscopic design meant that in certain conditions they could range on a target enshrouded by smoke. The German equipment was not superior in range to the British Barr & Stroud rangefinder found in the newest British capital ships, and, unlike the British range finders, the German range takers had to be replaced as often as every thirty minutes, as their eyesight became impaired, affecting the ranges provided to their gunnery equipment.