Year	mmol per litre
1980	4.942
1981	4.949
1982	4.953
1983	4.955
1984	4.954
1985	4.95
1986	4.942
1987	4.932
1988	4.926
1989	4.916
1990	4.909
1991	4.906
1992	4.904
1993	4.904
1994	4.907
1995	4.91
1996	4.913
1997	4.915
1998	4.916
1999	4.913
2000	4.908
2001	4.898
2002	4.886
2003	4.873
2004	4.861
2005	4.851
2006	4.842
2007	4.836
2008	4.828