How a base quantity a meter is evolved

In 1978, new born republic of France established a new system of weights and measurement. It's cornerstone was a meter, defined  to be a one tenth million of the distance from the north pole to the equator.

Later for practical resone this earth standard was abandoned and meter came to be defined as a distance between the fine line engraved near the end of the platinum-iridium bar, the standard meter bar, which is kept at international bureau of weights and measurement near Paris.

then due to some problem again the meter is defined in 1960, based on wavelength of light, was adapted. The standard of meter was redefined to be  1 650 763.73 wavelength of particular orange red light emitted by atom of krypton-86.

And then for more precision

Meter is defined as the length of the path of light in a vacuum during a time interval of 1/299 792 458 of asecond