The gap between 20 and 30 is usually around 1/4 in. You will have to just get out to the range and sight in. No software is dynamic enough to compute all the varialbles associated with that formula. How fast are you shooting, or what is your bow and arrow type, size, and length?
I have had good luck using On-Target2 software to set my pin gaps and I believe you can use Archer's Advantage to do that also but I haven't tried with that software. I have found that, although OT2 does a good job, I prefer doing it manually in the same fashion that Ben/PA does it. Set my first pin by adjusting the sight and then set the rest of the pins by adjusting each pin.
I have seen a pin gap chart based on the arrow weight and arrow speed. You need to set your 20 yard pin and then you can print out a graph and set the rest of your pins. This is not exacted but is very close. You have to tweak in the pins to be dead nuts. This is a fast and easy way to set up pins. I would not hunt without tweaking in the pins, but is a good way to set up before you go to the range. Like I said I have seen these charts, but do not know were to get one.
Now that I think about it, a sheet of sorts did come with a Copper John site one time. It had suggestions according to FPS and a paper you could hold over your site up to a light. I still like the tried and true methods.
what's nice, is that you can get a general gap when setting up long distance pins initially and then follow that up by actually shooting it. At least that's what I've seen my proshop guy do for a friend of mine when he purchased a sight from him.
I set my twenty pin...and go off of that. with the thirty about 1/4 of an inch lower like BowHunter546 said. then so on dropping my gab just a little bit more each time.
