Year	mmol per litre
1980	4.985
1981	4.979
1982	4.969
1983	4.959
1984	4.949
1985	4.942
1986	4.935
1987	4.93
1988	4.923
1989	4.915
1990	4.91
1991	4.904
1992	4.9
1993	4.898
1994	4.899
1995	4.904
1996	4.908
1997	4.911
1998	4.912
1999	4.916
2000	4.921
2001	4.921
2002	4.924
2003	4.923
2004	4.921
2005	4.916
2006	4.91
2007	4.902
2008	4.895