The original standard of "1m" is one twentieth of the length of the prime meridian. That is, one tenth of the distance from the south pole or the north pole to the equator. However, because it was later discovered that the earth was not a right sphere, the definition of "1m" was changed to the standard length of the international rice prototype made of platinum-iridium alloy. Later, with the popularization of laser, the definition of "meter" was changed to take the wavelength multiple of light wave as the standard. However, due to the uncertainty principle, it is impossible for us to get accurate measurements of length and time at the same time. Therefore, in 1983, the international organization of weights and measures changed the definition of light speed to the length standard, and set the light speed at 299,792,458 m/s (whole).