Year | Definition |
---|---|
1793 | 1/10,000,000 of the distance from north pole to equator. |
1795 | Provisional prototype 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. |