The Metre

In the 18th century there were two aproaches to standardizing the unit used to measure length, the one that was adopted was to make the metre equal to the distance from the equator to the northpole through paris divided by 10,000,000. the other option considered was the length of a pendulum with a period of 2 seconds.

Years went by and the need for the metre to be based on a constant in the world was seen. The solution decided on by the BiPM(International Bureau of Weights and Measures) was to base the metre on the speed of light in a vacuum. The current definition of a metre is "the distance light travels in a vacuum in 1/299,792,458 second." This makes the speed of light exactly 299,792,458 meters per second.