Year	mmol per litre
1980	4.912
1981	4.909
1982	4.904
1983	4.896
1984	4.893
1985	4.887
1986	4.878
1987	4.872
1988	4.867
1989	4.864
1990	4.862
1991	4.861
1992	4.861
1993	4.863
1994	4.867
1995	4.864
1996	4.861
1997	4.861
1998	4.865
1999	4.871
2000	4.88
2001	4.887
2002	4.894
2003	4.899
2004	4.905
2005	4.912
2006	4.92
2007	4.926
2008	4.931