Year	mmol per litre
1980	5.04
1981	5.037
1982	5.033
1983	5.028
1984	5.022
1985	5.018
1986	5.012
1987	5.008
1988	5.003
1989	4.998
1990	4.991
1991	4.973
1992	4.95
1993	4.934
1994	4.926
1995	4.929
1996	4.931
1997	4.925
1998	4.919
1999	4.916
2000	4.917
2001	4.919
2002	4.919
2003	4.915
2004	4.91
2005	4.902
2006	4.895
2007	4.888
2008	4.881