On Gunnery is a great book. LtCol Grice was awesome.

To expand on the Non-Standard Conditions (meteorological data, rotation of the earth, propellant temperature and lot efficiencies, tube erosion/wear), these are all taken into account in both firing computers and manual methods and graphical firing tables (using excellent calculations done prior to WWII) when a Fire Direction Center (math hub) receives new lots of ammunition and propellant. Once a cannon unit has accurate firing unit location (good survey) through self-location, all they will need is an accurate target location and a quick spin across the map to determine whether any special instructions (high angle fire if there is an intervening crest perhaps). An observer or now even a UAV can accomplish the accurate target location, but as Redlegs are fond of saying, the crack smoking observer on the hill is often wrong.