Year	mmol per litre
1980	4.927
1981	4.93
1982	4.929
1983	4.921
1984	4.915
1985	4.914
1986	4.905
1987	4.892
1988	4.88
1989	4.865
1990	4.847
1991	4.83
1992	4.818
1993	4.811
1994	4.801
1995	4.794
1996	4.785
1997	4.778
1998	4.774
1999	4.766
2000	4.754
2001	4.746
2002	4.731
2003	4.723
2004	4.719
2005	4.718
2006	4.718
2007	4.72
2008	4.723