I know this is over, but this is how I think about it. A take the first attack's BAB from all class and prestige classes. I add them all up and consult the fighters progression table and use that. For example, a Rogue2/Bard2/Fighter5/Weapon Master 4 works like this, 1 (rogue) + 1 (bard) + 5 (fighter) + 4 (weapon master) = 11. looking at the fighter table, i see 11/6/1 and that's my attacks. this doesn't work for monks unarmed, but its a good rule of thumb. hope this helps someone