Year	mmol per litre
1980	5.05
1981	5.045
1982	5.041
1983	5.036
1984	5.029
1985	5.025
1986	5.019
1987	5.01
1988	5.001
1989	4.992
1990	4.981
1991	4.962
1992	4.932
1993	4.901
1994	4.87
1995	4.841
1996	4.816
1997	4.792
1998	4.77
1999	4.752
2000	4.736
2001	4.72
2002	4.708
2003	4.694
2004	4.682
2005	4.674
2006	4.669
2007	4.666
2008	4.665