Greetings,
To estimate range in a tank. Go off line. line up a shot on the gvs on the field. Make sure you are perpendicular to the flank of the tank.
Compare the size of the tank to the horizontal lines in the reticle. No matter the zoom, the tank will be the same size as compared to the reticle line.
It has been a while since I last did this, but, for example, I seem to remember that at 1000 a Pnzr was as long as the reticle line and as wide as half the line. Be warned, I haven't done this in year or so and I may not be remembering correctly. Also, a Tiger, Sherman and T34 have different length and width so you range may vary, but it should get you close.
Will this range estimation get you consistent 1st round hits? No. It will get you in the ball park.
Regards,