Data points in red are recommended value based on a review of the entire evidence. Data points in blue are results of torsion balance experiments (Cavendish experiment). Data points in green are from other types of experiments (two with pendulums, one with a beam balance and one [2014] from atom interferometry).

The 1911 value is from Poynting's article in Encyclopedia Britannica 1911 edition, it represents the best estimate made by Poynting at this time, but it essentially corresponds to Poynting's own result from 1891, which was the best available at that time. Only the upper half of Poynting's error bar is shown. Red values from 1969 onwards are the CODATA NIST recommended values.

The image illustrates how all experiments since the 1980s have remained inside the uncertainty of the 1969 recommended value, but have failed to converge on any more accurate value in spite of the citation of very optimistic uncertainty intervals in some experiments.

Literature: Schlamminger (2014), Schlamminger, Gundlach, Newman (2015), DeSalvo (2015)

Data:

meta:
1911	6.66		0.013	        Poynting EB1911
1969	6.6732		0.0031	        CODATA
1973	6.672		0.0049	        CODATA
1986	6.67449		0.00081	        CODATA
1998	6.673		0.001	        CODATA
2002	6.6742		0.0001	        CODATA NIST 2002
2006	6.67428		0.00067	        CODATA NIST 2006
2010	6.67384		0.0008	        CODATA  NIST 2010
2014	6.67408		0.00031	        CODATA NIST 2014

torsion:
1930	6.67		0.005	        Heyl 1930
1942	6.673		0.003	        Heyl and Chrzanowski  1942
1982	6.6726		0.0005 	        Luther and Towler 1982[1]
1996	6.6729		0.0005          Karagioz and Izmailov 1996[2]
1997	6.6740		0.0007	        Bagley and Luther 1997[3]
2000	6.674215 	0.000092        Gundlach and Merkowitz 2000[4]
2001	6.67559		0.00027	        Quinn et al. 2001[5]
2003	6.67387		0.00027		Armstrong and Fitzgerald 2003[6]
2010	6.67349		0.00018	      	Tu et al. 2010[7]
2013	6.67545		0.00018		Quinn et al. 2013[8]
2014	 6.67433	0.00013	 	Newman et al. 2014 [9] [not shown]

other:
2002	6.67422		0.00098		Kleinevoss 2002[10] (two pendulums)
2006	6.674252 	0.000122 	Schlamminger et al. 2006[11] (beam balance)
2010	6.67234		0.00014  	Parks and Faller 2010[12] (two pendulums)
2014	6.67191		0.00099	 	Rosi et al. 2014 (atom interferometry)[13]