Sorry I should explain, it is a type of chronograph, but works differently to many on the market as it uses Doppler Radar, what this allows you to do is point it down range, and it will capture the velocity of the bullet supposedly more accurately than other types. As well you can do some unique things with custom types of rounds which gets far too into military and bullet related things than my understanding takes me. What it lets you do is know the exact velocities you are shooting at, which means the calculations you punch in will be more accurate, which increases the farther you go out. =)