Year	mmol per litre
1980	4.951
1981	4.949
1982	4.946
1983	4.938
1984	4.934
1985	4.931
1986	4.929
1987	4.93
1988	4.926
1989	4.914
1990	4.9
1991	4.886
1992	4.873
1993	4.861
1994	4.856
1995	4.854
1996	4.851
1997	4.849
1998	4.845
1999	4.842
2000	4.837
2001	4.831
2002	4.825
2003	4.815
2004	4.804
2005	4.79
2006	4.776
2007	4.764
2008	4.753