I use the level level level kit to insure my reticle is perpendicular to the bore of my rifle and have a level mounted on my scope once it's leveled. When I zero my rifle I make sure I shoot east or west to take out any type of corrialis effect and it maybe minuscule at close ranges but Believe it or not it makes a difference when shooting at extremely long ranges. Spin drift is another element to account for. I can shoot upto 1 mile here on our farm but rarely shoot that far. I usually shoot out to 1500 yards.