Hello Gents , I have 4-16x50 wide angle zero option scope on my webley fx 2000 . my question is the scope has on the other end from the magnification, adjustment for range 10-15 -20 out to 100 yards , does this really work do i have to keep adjusting or is it just a gimmick ? never had a scope like this before ,and i've hardly used it since i bought it a few years ago got it to keep my chickens safe from Mr Fox. as you can guess I don't know much about these new fangled scopes not like the open sights i had on my old BSA Meteor lol ... thanks in advance of any replies ..