Year	mmol per litre
1980	4.774
1981	4.765
1982	4.755
1983	4.75
1984	4.741
1985	4.727
1986	4.714
1987	4.703
1988	4.696
1989	4.692
1990	4.689
1991	4.686
1992	4.682
1993	4.679
1994	4.677
1995	4.676
1996	4.674
1997	4.675
1998	4.675
1999	4.675
2000	4.679
2001	4.682
2002	4.686
2003	4.689
2004	4.692
2005	4.693
2006	4.696
2007	4.697
2008	4.699