Year	mmol per litre
1980	4.142
1981	4.12
1982	4.1
1983	4.084
1984	4.067
1985	4.055
1986	4.047
1987	4.037
1988	4.03
1989	4.024
1990	4.015
1991	4.006
1992	3.996
1993	3.984
1994	3.968
1995	3.954
1996	3.94
1997	3.926
1998	3.912
1999	3.9
2000	3.889
2001	3.877
2002	3.869
2003	3.868
2004	3.877
2005	3.888
2006	3.897
2007	3.906
2008	3.912