Year	mmol per litre
1980	4.195
1981	4.185
1982	4.172
1983	4.16
1984	4.139
1985	4.119
1986	4.1
1987	4.075
1988	4.054
1989	4.032
1990	4.011
1991	3.994
1992	3.977
1993	3.962
1994	3.947
1995	3.932
1996	3.919
1997	3.908
1998	3.895
1999	3.881
2000	3.869
2001	3.862
2002	3.853
2003	3.846
2004	3.843
2005	3.835
2006	3.826
2007	3.812
2008	3.801