Year	mmol per litre
1980	5.257
1981	5.228
1982	5.199
1983	5.164
1984	5.128
1985	5.092
1986	5.06
1987	5.029
1988	5.001
1989	4.97
1990	4.941
1991	4.917
1992	4.897
1993	4.881
1994	4.863
1995	4.846
1996	4.832
1997	4.823
1998	4.816
1999	4.809
2000	4.805
2001	4.804
2002	4.802
2003	4.796
2004	4.799
2005	4.804
2006	4.816
2007	4.828
2008	4.841