19th century physicist Leon Foucault's low-tech approach to measuring the speed of light involved a candle, set at an angle to a steadily rotating mirror, and a stationary mirror placed some distance away. The lights reflected off the rotating mirror, and then the stationary mirror, and then back to the rotating mirror, which would have moved a set amount by that time. The speed of light—well, technically, the time it took for light to cross the distance between the mirrors—could be easily calculated by looking at the angles of the reflections on the rotating mirror.

This simple and instructive set-up is still used by teens across the world in school, although they usually use lasers, not a candle. You can even buy the hardware to do the experiment online. As you can imagine, these designs are somewhat inaccurate and imprecise because they use outdated measurement tools like microscope rulers, meaning they can usually only get to within five percent of the accepted value for the speed of light.

That's why Gregor Weihs and Zoltán Vörös, professors at the University