Year	mmol per litre
1980	4.862
1981	4.845
1982	4.826
1983	4.806
1984	4.788
1985	4.771
1986	4.755
1987	4.741
1988	4.729
1989	4.716
1990	4.705
1991	4.695
1992	4.689
1993	4.686
1994	4.685
1995	4.687
1996	4.69
1997	4.694
1998	4.699
1999	4.705
2000	4.707
2001	4.709
2002	4.709
2003	4.709
2004	4.708
2005	4.708
2006	4.708
2007	4.708
2008	4.709