The reticle isn't centered in that scope.......as the elevation is adjusted, it moves......
Windage adjustment is in the mount (LSR/SSR/Turret/Claw/Etc....)
the small knob/nut on top of the elevation turret is the paralax/focus adjustment
as far as zeroing, since the turret doesn't have range markings, you use the white line to establish a set distance......say one or two hundred yards.....loosen the set screw at the rear of the turret, adjust the elevation till you're zeroed at your favorite shooting distance, then without moving the turret, loosen (slightly) the 3 small screws on top of the turret, loosen the set screw, rotate the outer ring till the white line lines up with the turret set screw, then retighten the 3 screws.....that way whenever the white line is lined up with the set screw, you know what distance your elevation is set for...