As an addition: Although the "idea of 'instantaneous velocity'" was develped by the Oxford Calculators, it was the School of Orseme (Nicole Oresme, Paris, 14th century) that gave a mathematical (i.e., graphical) proof for the "Merton Mean Speed Theorem". It was less the Oxford Calculators but the School of Orseme that rendered the Aristotelian concept of motion (impetus theory) obsolete. The main reason for the development of a new theory of motion of flying heavy objects was that the Aristotelian impetus theory was unsuited to adequately calculate trajectories of projectiles in military combat, esp. against fortresses.