Year	mmol per litre
1980	4.225
1981	4.216
1982	4.2
1983	4.185
1984	4.167
1985	4.142
1986	4.12
1987	4.1
1988	4.077
1989	4.061
1990	4.046
1991	4.029
1992	4.015
1993	4.002
1994	3.99
1995	3.981
1996	3.974
1997	3.968
1998	3.964
1999	3.962
2000	3.96
2001	3.96
2002	3.962
2003	3.964
2004	3.965
2005	3.968
2006	3.972
2007	3.975
2008	3.979