Year	mmol per litre
1980	4.803
1981	4.793
1982	4.786
1983	4.78
1984	4.778
1985	4.776
1986	4.774
1987	4.773
1988	4.773
1989	4.775
1990	4.778
1991	4.779
1992	4.783
1993	4.784
1994	4.782
1995	4.782
1996	4.779
1997	4.779
1998	4.776
1999	4.775
2000	4.773
2001	4.77
2002	4.772
2003	4.771
2004	4.772
2005	4.773
2006	4.778
2007	4.78
2008	4.782