In 1676, Ole Rømer became the first to prove that light travels at a finite speed by observing the eclipses of Jupiter's moon, Io. While his result of 214,000 km/s holds a ~28% margin of error compared to the modern value of 299,792.458 km/s, the methodological breakthrough was profound, forever altering our perception of the cosmos. Over the past 350 years, the transition from Rømer’s early observations to modern laser interferometry reflects a monumental leap in precision—narrowing the measurement uncertainty from thousands of kilometers to mere decimeters. This ranking chronicles not just a physical constant, but the evolution of human technological limits.