Actually, if you are REALLY anal, you figure out how much out of balance the prop is, mount it as Dennis says, use a meter to measure the engine vibration (they exist, but I forget the name), and then test various amounts of "out of balance" until you get the smoothest running engine. Then you adjust all your props to that setting.



Have fun. Me, I usually just bolt them on and fly. But then again, I fly combat, so I can easily spend more time balancing a prop than I would flying it before it gets broken in a mid-air