|1793||1/10,000,000 of the distance from north pole to equator.|
|1795||Provisional meter bar constructed from brass.|
|1799||Prototype meter bars constructed from platinum.|
|1889||International prototype meter bar constructed
from platinum-iridium. |
It was an X-shaped cross section bar.
|1906||1,000,000/0.64384696 wavelengths of the red line of the cadmium spectrum.|
|1960||1,650,763.73 wavelengths of radiation emitted
during the transition |
between levels 2p10 and 5d5 of the krypton-86 atom.
|1983||Length traveled by light in a vacuum during 1/299,792,458 of a second.|