Year	mmol per litre
1980	4.733
1981	4.729
1982	4.72
1983	4.712
1984	4.701
1985	4.693
1986	4.683
1987	4.676
1988	4.671
1989	4.664
1990	4.653
1991	4.646
1992	4.643
1993	4.648
1994	4.651
1995	4.653
1996	4.656
1997	4.656
1998	4.653
1999	4.651
2000	4.648
2001	4.642
2002	4.638
2003	4.633
2004	4.63
2005	4.627
2006	4.624
2007	4.622
2008	4.621