IBO rates a 70# bow at 30" draw with an arrow that is 5 grains per # bow weight equaling 350 grains, therefore high speeds. AMO rates a 60# bow at 30" draw with an arrow that is 9 grains per # bow weight equaling 540 grains, therefore the lower speeds. AMO now also has a test for the same 60# bow at 6 grains per # bow weight equaling 360 grains. AMO dos'nt approve of the IBO test, it puts the bow too close to the danger zone.