Mr. Norb Mullaney, a professional engineer, is recognized as the leading authority on the physics of bows and endows. He states that "The hand held bow has one characteristic that distinguishes it from a crossbow or any type of firearm. The internal ballistics are a function of the shooter, his or her physical geometry and capabilities, shooting form, consistency and reaction to stress and trauma. In the crossbow and firearms, the internal ballistics are fixed. The action of the shooter in triggering a release of energy does nothing more than initiate a process that is consistent and repetitive. The hand held bow is different. Every action of the shooter contributes something either positive or negative to the interior ballistic process. As the interior ballistics vary, so do the exterior ballistics. Shooting the hand held bow and arrow is much more complicated than aiming a fixed system of ballistics and touching off the energy discharge. The total energy to draw, hold and release the bow must come directly and unassisted from the shooter's muscle power."