The large kob on left is used to tighten the sight to the base. If you look real close at lower left hand corner you will see an adjustment screw. Also the aperture can be unscrewed-and different aperatures can be used. Also loosening the aperture allows you to set elevation. I prefer to leave rear sights centered, and make slight windage adjustments with the front bead-so I have never adjusted mine for windage. But if they say it is so, then it is so. The Quality is second to none. The only problem you might have is with front sight height. If you order from NECG it may cost a couple of extra bucks, but they can calculate front bead height for you. Tom.