Chronograph?

Take a look at this article...

http://www.pyramydair.com/article/Who_needs_a_chronograph_August_2006/31

Sure, a chronograph measures the speed of a projectile using light. There are 2 (sometimes more) photo sensors that face the sky and read the shadow of the projectile as it passes over them and calculates the speed then gives you a read out. It is necessary to know the speed of your pellet if you are trying to tune your gun, otherwise you are just guessing. It can also help with diagnosing problems. It is an indispensable tool for tuning.

kyler as mentioned a chronograph can be invaluable for determining the best fill levels for your unregulated pcp rifles. I went out a few days ago with my TalonSS with a new pellet to determine the best power wheel setting where dialing higher just wastes air. Determining starting fill pressures for a tight bell curve and when the end pressure and velocities dropped off. I also determined the best start and end pressures for a fairly tight 20 fps spread for approximately 40 shot string. I also shot the rifle at the muzzle and 23 yards my first cross over point to get to velocities to determine my pellet B.C. using the ChairGun Pro software which is free to download. Using ChairGun with the inputs from the chronograph and other measurements you can print out drop charts and get scope setting for clicks, drop, mil dots and point blank zero for your kill zone size among other things. Here is the link to the ChairGun Pro download and if you get on youtube you can watch some tutorials on its use. Bill
http://www.hawkeoptics.com/chairgun.html 

I shot pellet guns since I was a kid into college and never had a chrony. Couldn't really understand why I'd need one now that I'm back into the hobby all these years later but honestly a chrony is just about as important as you gun and pellets. Have pellets flying all over the target? Constantly adjusting your scope? The chrony won't tell what is wrong with your gun but it certainly can tell you that something is wrong with your gun. My shots were wandering and I discovered a lose screw so I tightened it and they got better but were still wild at times. Putting my gun through the chrony revealed my fps had fallen from 830's to 530's. I can't see that w/my eye but the chrony can.

Chrony is a must if you plan to use Strelok or Chairgun apps. Gotta have those numbers if you plan to get accurate info from the tool.

Besides what has been said above a chronograph allows you to isolate your overall best performing shots based on pressure in your PCP air rifle. In other words an unregulated PCP air rifle will normally shoot a Bell curve over the entire range of available shots or it may just be a declining line as pressure decreases per shot. Example would be that on shot number 3 through 12 you have the closest FPS Spread out of say 20 shots. You can view the manometer pressure of your rifle at shot 3 through 12. So you only need to fill your rifle to the manometer pressure of your number 3 shot and the next up to shot 12 in your string would be the most consistent shots with the smallest spread. I am speaking very simplistic with this analogy of an unregulated rifle and the acceptable spread could easily be over many more shots in a string. That consistency would give you the best chance of striking your target with the same point of impact for the pressure and yardages you have chosen. You may want to attempt to tune those numbers by adjusting your hammer spring up or down with turns of a hex wrench or in conjunction with the striker length another size hex wrench to flatten your Bell Curve to achieve more shots within a consistent pressure range over your shot string.
The Chair Gun App allows you to enter your numbers to give you a visual depiction of bullet drop (pellet drop) for increasing distance from the muzzle. This gives you a value to hold above your POI (point of impact) for the distance that you have sighted the rifle to. Or you can use those Chair Gun values to determine the number of clicks up or down to move your POI for a more distant shot (yards or meters) from your base zero. This technique will keep your crosshairs zeroed on the target (doping the scope) at more distant targets instead of using Hold Over by the value read from the Chair Gun values.
I hope I have not confused you and there are many variables but just trying to keep it simple. The chronograph is a great tool to let you know values that you can enter into the Chair Gun program as well as let you adjust your rifle (tune).

Kyler, it would be great if you could get up with one of these AGN members nearest you. It would all seem easy if some one walked you through obtaining the info.and appling it into a program. Your shooting accuracy will amaze you.