Year	mmol per litre
1980	4.721
1981	4.716
1982	4.711
1983	4.704
1984	4.696
1985	4.687
1986	4.679
1987	4.671
1988	4.667
1989	4.661
1990	4.656
1991	4.653
1992	4.653
1993	4.653
1994	4.652
1995	4.65
1996	4.645
1997	4.637
1998	4.628
1999	4.62
2000	4.613
2001	4.603
2002	4.593
2003	4.582
2004	4.571
2005	4.562
2006	4.549
2007	4.541
2008	4.534