Year	mmol per litre
1980	4.784
1981	4.783
1982	4.782
1983	4.782
1984	4.782
1985	4.782
1986	4.781
1987	4.778
1988	4.776
1989	4.775
1990	4.775
1991	4.774
1992	4.774
1993	4.774
1994	4.777
1995	4.78
1996	4.784
1997	4.791
1998	4.799
1999	4.809
2000	4.82
2001	4.83
2002	4.839
2003	4.851
2004	4.862
2005	4.873
2006	4.886
2007	4.901
2008	4.916