Year	mmol per litre
1980	4.962
1981	4.964
1982	4.968
1983	4.972
1984	4.981
1985	4.991
1986	4.999
1987	5.004
1988	5.009
1989	5.014
1990	5.018
1991	5.02
1992	5.024
1993	5.027
1994	5.028
1995	5.028
1996	5.028
1997	5.026
1998	5.021
1999	5.015
2000	5.006
2001	4.999
2002	4.99
2003	4.979
2004	4.969
2005	4.96
2006	4.951
2007	4.944
2008	4.938