Year	mmol per litre
1980	4.956
1981	4.946
1982	4.933
1983	4.921
1984	4.91
1985	4.899
1986	4.889
1987	4.879
1988	4.864
1989	4.848
1990	4.831
1991	4.812
1992	4.796
1993	4.779
1994	4.762
1995	4.747
1996	4.731
1997	4.716
1998	4.701
1999	4.688
2000	4.682
2001	4.673
2002	4.666
2003	4.659
2004	4.651
2005	4.644
2006	4.64
2007	4.638
2008	4.638