After the first round
Below the target, enter where the round landed. Plus means too far, minus means too short, plus the deviation left or right. The calculator shifts the aiming point and gives you the new elevation at once.
Under every solution it says how many mils 10 m more range cost. That lets you correct in your head when it has to be quick.
Grenzen
The maths uses measured reference values and estimates in between. That is good to within a few metres, but it does not replace a spotter.
Height differences and dispersion are not included. If the target sits higher than the gun, the round lands short.
Below 110 m the mortar has a dead zone, the artillery below 786 m.