The efficiency of bows also varies. Normally between 70–85% of the stored energy is transferred to the arrow. This stored energy is referred to as potential energy. When transferred to the arrow it is referred to as kinetic energy. The product of S.E./P.D.F. and efficiency can be called the power factor. There are two measurement standards of this quantity – AMO and IBO speed. AMO is defined as the initial velocity of a arrow when shot from a bow with a peak draw weight of and draw length . IBO speed is defined as the initial velocity of a arrow shot from a bow with a peak draw weight of and a draw length of .