I’ve sat in more than a couple mortar pits in my time, and have pulled rear security for sniper teams.
There’s always technical solutions, ballistic calculators, holds for known targets on mortars, etc, but absolutely no way you’ll catch charlie or a sniper not capable of the mental math to run their weapon system.
Mortars; often they just drive around with truck mounted systems and get sent coords, pull out a map and start calculating, snipers range find and then adjust with the markings in their scopes via mental math. They don’t dial their scope to 648 meters or whatever you’re thinking. I’ll admit I’m less clear on sniper math, but they usually all have notepads with them on performance data, DOPE, of their weapons systems to make needed adjustments to their calculations.
I do want to be clear that the math isn’t crazy, and there’s often tech solutions available, but it’s definitely trained and often practiced.