Year	mmol per litre
1980	4.949
1981	4.938
1982	4.931
1983	4.92
1984	4.909
1985	4.897
1986	4.885
1987	4.877
1988	4.868
1989	4.86
1990	4.859
1991	4.859
1992	4.859
1993	4.859
1994	4.86
1995	4.86
1996	4.861
1997	4.863
1998	4.863
1999	4.864
2000	4.865
2001	4.866
2002	4.865
2003	4.863
2004	4.866
2005	4.866
2006	4.869
2007	4.872
2008	4.876