Year	mmol per litre
1980	4.221
1981	4.202
1982	4.182
1983	4.161
1984	4.14
1985	4.119
1986	4.1
1987	4.082
1988	4.065
1989	4.049
1990	4.03
1991	4.015
1992	3.998
1993	3.975
1994	3.959
1995	3.945
1996	3.932
1997	3.921
1998	3.914
1999	3.907
2000	3.9
2001	3.892
2002	3.886
2003	3.883
2004	3.878
2005	3.872
2006	3.869
2007	3.865
2008	3.863