Hi, mundumugu:
Just leave it set to G1 for ordinary bullets. That's good enough out past 400 yards/meters. It's a complex function, but if you want, I'll go into more detail later.
Just one point now. A bullet with a ballistic coefficient of .4 when using the G1 function can have a very different ballistic coefficient with another (G5,G6,G7, etc.) It could be .2 or .8.
Bye
Jack