RGA sergeant copying down instructions for SOS lines, Monchy-le-Preux, 18 March 1918. The quantity of data the sergeant has to record shows some of the technological advances the Royal Artillery made during the war. In addition to this information, recent meteorological information would have to be considered, and each gun's individual wear would have to be factored in as well.
In defensive fire this was paradoxically somewhat less important than attacking, because defensive fire that came to friendly troops at least did so while they were in cover. However, accuracy in bombarding and counter-battery fire was extremely important.
Source: IWM photo Q10895.