You need:- the distance to the target- the distance between the iron sights of your weapon. Then just enter how far you missed the goal - how far you go up or down, to the right or left of the shot into the black.The app will tell you the necessary settings to your front sight or rear sight to get your iron sights aligned. That's how easy it is.***If you want it even more simple: Click adjustment!Perhaps your weapon has an adjustment screw that clicks when you turn it. A small sign tells you the amount of adjustment for one click, usually in MoA (for example "1/4 MoA), where 1 MoA = (1/60) °.Then you can choose "click adjustment", choose the number of MoA (e. g. "1/4 MoA") and the app will tell you the number of clicks you have to do. So you won't need any measuring instrument. ***The app works in the measuring units you want: You can choose between metric units (m, cm, mm) yard, foot and inches. Your last choice will be saved on your device, so you will have little entering work the next time you use the app.