Year	mmol per litre
1980	4.8
1981	4.799
1982	4.799
1983	4.796
1984	4.792
1985	4.788
1986	4.784
1987	4.78
1988	4.778
1989	4.778
1990	4.776
1991	4.777
1992	4.78
1993	4.784
1994	4.788
1995	4.788
1996	4.787
1997	4.783
1998	4.778
1999	4.772
2000	4.767
2001	4.758
2002	4.749
2003	4.739
2004	4.729
2005	4.719
2006	4.707
2007	4.699
2008	4.691