It sounds like you have a Bushnell Banner that has both a bullet drop compensator and a range finder. That number you see increasing at the top of the scope as you increase magnification is the distance in yards, measured via the 18 inch space between the stadia wire above the crosshair & the crosshair(18 inches being the average size of a deers body bracketed between those stadia wires). The Bullet Drop Compensator is in the up/down sight adjustment at the top of the scope. You unscrew the top adjustment cap with a nickel or dime(gently, it's made of plastic and breaks easily) and inside is the BDC dial with teeth or little serrations on the bottom that fits into teeth on the scope adjustment. The scopes used to come with 4 of those BDC dials, #1,2, and 3 premarked with distance numbers depending on the trajectory of the caliber the scope is going on and, and a 4th that was blank, that you could mark yourself in the event you worked up a special reload. What you do is, you remove the BDC dial, and manually sight the gun in for 100 yards. Then you insert the correct number BDC dial(depending on caliber you have) with the '100' showing through the clear little window, making sure the teeth make solid contact with the teeth in the scope. Then GENTLY tighten the cap cover with your nickel or dime. Now once you bracket your deer and determine the distance as will show in that top number you mentioned, then you turn the bullet drop compensator knob on that top scope adustment, till the correct distance shows in the little window on the back of the adjustment knob, hold dead on and fire.
I actually have an original owners manual with all the instructions & directions(circa 1982), and BDC dials #1 & 2,(which cover about 90% of all the rifle calibers), and the blank one for working up a reload, brand new, never used, you're welcome to them if you need them. Let me know.
