I gotta agree with the guys above, when a true shooter comes into range, there is no doubt about it. No sizing him up. It's instantly OMG and then immediately tend to the task at hand. If you find yourself questioning how big it is, 99.9% of the time it's not going to end up being what you were truly wanting to harvest when you walk up on him. You need to make a firm commitment to spending day upon day of letting deer walk. Not just one or two, but many.It isn't easy,especially if you live in an area wherebig deer are scarce.If you let a few yearlings go by for a few days but thenbecome impatient and shoot the next bigger buck that walks by, you will end up harvesting a buck that is below the goal that you actually had in mind. Most of us have been there. It may sound like a broken record, but you can't shoot a P&Y buck if you shoot a smaller one first.
Also, the most important piece of the puzzle you are putting together is hunting in an area where those bucks exist and call home. Do your summer scouting. If you are thorough and see no trulybig bucks before the season starts, it may be time for a new/better spot.