text: Timeline of definition\n\n    * 1790 May 8 — The French National Assembly decides that the length of the new metre would be equal to the length of a pendulum with a half-period of one second.\n\n    * 1791 March 30 — The French National Assembly accepts the proposal by the French Academy of Sciences that the new definition for the metre be equal to one ten-millionth of the length of the Earth's meridian along a quadrant, that is the distance from the equator to the north pole.\n\n    * 1795 — Provisional metre bar constructed of brass.\n\n    * 1799 December 10 — The French National Assembly specifies that the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives, as the final standard.\n\n    * 1889 September 28 — The first General Conference on Weights and Measures (CGPM) defines the length as the distance between two lines on a standard bar of an alloy of platinum with ten percent iridium, measured at the melting point of water.\n\n    * 1927 October 6 — The seventh CGPM adjusts the definition of the length to be the distance, at 0°C, between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard atmosphere of pressure and supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 millimetres from each other.\n\n    * 1960 October 20 — The eleventh CGPM defines the length to be equal to 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.\n\n    * 1983 October 21 — The seventeenth CGPM defines the length as equal to the distance travelled by light in vacuum during a time interval of 1/299 792 458 of a second.