Year	mmol per litre
1980	4.988
1981	4.964
1982	4.942
1983	4.922
1984	4.899
1985	4.875
1986	4.857
1987	4.844
1988	4.833
1989	4.823
1990	4.815
1991	4.809
1992	4.803
1993	4.798
1994	4.791
1995	4.783
1996	4.777
1997	4.772
1998	4.767
1999	4.76
2000	4.754
2001	4.747
2002	4.742
2003	4.735
2004	4.727
2005	4.719
2006	4.709
2007	4.703
2008	4.696