By flying planned parameters using the depressed sight... just like with early F-4's and many other aircraft
The A-10 was planned as a relatively cheap tank killer, relying on Maverick missiles and the big gun
with fast bullets = flat bullet trajectory = easy to hit with it
Bombing tanks, troops etc would have been done with CBU's which make good part of the aim error of manual
bombing
To make flying planned parameters easier the whole HUD symbology depressed together with the gunsight, keeping
airspeed - pipper - altitude all in one line = making it easy to read
I couldnt do that in my mod due to game limitations, but I claim that it "looks OK"