the 2 lines at the top of the scope are made to be calibrated for a deer , from the top of bis back to the bottom of the chest .
i beleive it is suposed to be 16 inches
so if you come across a deer sized animal at a unknown distance , you adjust the magnification till his body fits between the 2 lines , then you have a rough estimate on the distance .
some of them have special numbered turrets for the elevation knob for different rounds .
what i did with my stw was i zero'd it to 100 yards , marked the elevation knob , zero'd it to 200 , marked the knob , same for 300 , 400 and 500 yards .
so i would use the 2 lines on the top of the scope , figure out the range , then adjust the elevation knob to the coresponding mark for that range , then fire directly into the animals body without holding over .
fool proof .... not even close ............. if set up properly by someone who understands how it is suposed to work , it is at best a secondary piece of information to help the shooter determine the range of the animal .
but i do love the older redfield widefield scopes .