Year	mmol per litre
1980	4.837
1981	4.819
1982	4.801
1983	4.782
1984	4.764
1985	4.742
1986	4.718
1987	4.695
1988	4.674
1989	4.656
1990	4.638
1991	4.622
1992	4.608
1993	4.595
1994	4.586
1995	4.58
1996	4.576
1997	4.574
1998	4.572
1999	4.57
2000	4.568
2001	4.565
2002	4.56
2003	4.556
2004	4.552
2005	4.548
2006	4.544
2007	4.541
2008	4.539