knowing anything about true target aquisition and ranging long distance shots helps, but i understand not all of you are Marines and most havent been hounded with training for this over many years so to break it down barney style for most of you look at this http://www.mil-dot.com/user-guide helps explain how to gauge distance of targets using simple formulas used by the USMC, USArmy, USNavy and anyone using a mil-dot equipped scope... hope this helps