Year	mmol per litre
1980	4.951
1981	4.919
1982	4.894
1983	4.87
1984	4.845
1985	4.822
1986	4.799
1987	4.777
1988	4.749
1989	4.726
1990	4.707
1991	4.684
1992	4.667
1993	4.649
1994	4.635
1995	4.623
1996	4.613
1997	4.606
1998	4.601
1999	4.598
2000	4.597
2001	4.594
2002	4.589
2003	4.585
2004	4.582
2005	4.577
2006	4.572
2007	4.569
2008	4.566