I'm getting ready to setup a new scope. The first step after mounting a large comma parallax wheel is to note the yardage on the wheel tape. What do you use to focus on to mark your parallax wheel? I have used several different items with limited success. Last time I used a cereal box next to my squirrel knockdown target. My thought was the print on the box would help refine my adjustments but this turned out to be a total fail. The print was not as sharp as I would have liked. DO they make a background target just for this part of setting up a new scope? I would appreciate your experiences. Thanks