Year	mmol per litre
1980	5.067
1981	5.055
1982	5.043
1983	5.029
1984	5.016
1985	5.001
1986	4.99
1987	4.977
1988	4.962
1989	4.95
1990	4.939
1991	4.926
1992	4.906
1993	4.894
1994	4.881
1995	4.867
1996	4.841
1997	4.82
1998	4.806
1999	4.795
2000	4.78
2001	4.761
2002	4.739
2003	4.717
2004	4.703
2005	4.686
2006	4.668
2007	4.659
2008	4.657