Metre
Timeline

Metre

Section Title: Timeline
Table Section Text: None

Basis of definition	Date	Absolute uncertainty	Relative uncertainty

1/10 000 000 part of the quadrant along the meridian, measurement by Delambre and Méchain (443.296 lines)	1795	500–100 μm	10−4

First prototype Mètre des Archives platinum bar standard	1799	50–10 μm	10−5

Platinum-iridium bar at melting point of ice (1st CGPM)	1889	0.2–0.1 μm (200–100 nm)	10−7

Platinum-iridium bar at melting point of ice, atmospheric pressure, supported by two rollers (7th CGPM)	1927	n.a.	n.a.

Hyperfine atomic transition; 1650763.73 wavelengths of light from a specified transition in krypton-86 (11th CGPM)	1960	4 nm	4×10−9

Length of the path travelled by light in a vacuum in 1/299 792 458 second (17th CGPM)	1983	0.1 nm	10−10

Sentence(s)

In 1960, the 11th CGPM defines the metre as 1650763.73 wavelengths from a transition in krypton-86 atom.

final_sentence: In 1960, the 11th CGPM defines the metre as 1650763.73 wavelengths from a transition in krypton-86 atom.