Year	mmol per litre
1980	4.752
1981	4.739
1982	4.724
1983	4.708
1984	4.693
1985	4.675
1986	4.656
1987	4.637
1988	4.621
1989	4.605
1990	4.591
1991	4.576
1992	4.565
1993	4.554
1994	4.542
1995	4.535
1996	4.535
1997	4.553
1998	4.574
1999	4.601
2000	4.628
2001	4.662
2002	4.695
2003	4.725
2004	4.755
2005	4.778
2006	4.793
2007	4.807
2008	4.817