Year	mmol per litre
1980	4.976
1981	4.975
1982	4.975
1983	4.977
1984	4.977
1985	4.977
1986	4.974
1987	4.971
1988	4.964
1989	4.957
1990	4.952
1991	4.944
1992	4.935
1993	4.927
1994	4.919
1995	4.91
1996	4.9
1997	4.892
1998	4.883
1999	4.873
2000	4.867
2001	4.858
2002	4.849
2003	4.841
2004	4.837
2005	4.832
2006	4.827
2007	4.821
2008	4.816