The control position for the main armament were located in the spotting tops at the head of the foremast. Data from a Barr and Stroud coincidence rangefinder located there was input into a Dumaresq mechanical computer and electrically transmitted to Vickers range clocks located in the transmitting station located beneath each position on the main deck, where it was converted into range and deflection data for use by the guns. The target's data was also graphically recorded on a plotting table to assist the gunnery officer in predicting the movement of the target. The turrets, transmitting stations, and control positions could be connected in almost any combination. By 1912, another nine-foot rangefinder was added at the forward side of the compass platform. In late 1914, more nine-foot rangefinders, protected by armoured hoods, were installed on the turret roofs.