Oresme in Paris did it graphically. The calculators apparently produced the "mean speed theorem". It's written in the full text of the paper: "The “Oxford calc

Oresme in Paris did it graphically. The calculators apparently produced the "mean speed theorem". It's written in the full text of the paper: "The “Oxford calculators” of the 14th century CE, who were centered at Merton College, Oxford, are credited with formulating the “Mertonian mean speed theorem” for the distance traveled by a uniformly accelerating body, corresponding to the modern formula s = t•(v0 + v1)/2, where v0 and v1 are the initial and final velocities (12, 13). In the same century Nicole Oresme, in Paris, devised graphical methods that enabled him to prove this relation"