Quoted:
I centered the dot above the front blade  to start (lower 1/3 co-wittness on AR-15 flat top) and went from there. It took no more that 6 rounds to zero at 100 yards with the 2x.  I mounted it on a cantilevered LaRue LT129 and put about 100 rounds down range with no problems.  Then I took the mount and sight off and replaced it and it held zero.  With the 2x removed I had no problem hitting the paper right where I put the dot at the same yardage.  It was easier to see the green dot than the red.  The day was full sun and bright.  Over all I am very pleased with the sight.