An important development was the Zone Call procedure in 1915. By this time maps were 'squared' and a target location could be reported from the air using alphanumeric characters transmitted in Morse code. Batteries were allocated a Zone, typically a quarter of a mapsheet, and it was the duty of the RFC signallers on the ground beside the battery command post to pick out calls for fire in their battery's Zone. Once ranging started the airman reported the position of the ranging round using the clock code, the battery adjusted their firing data and fired again, and the process was repeated until the pilot observed an on-target or close round. The battery commander then decided how much to fire at the target.