Year	mmol per litre
1980	5.117
1981	5.106
1982	5.091
1983	5.079
1984	5.066
1985	5.054
1986	5.042
1987	5.031
1988	5.023
1989	5.017
1990	5.014
1991	5.009
1992	4.994
1993	4.964
1994	4.943
1995	4.931
1996	4.92
1997	4.914
1998	4.912
1999	4.905
2000	4.906
2001	4.905
2002	4.909
2003	4.906
2004	4.903
2005	4.905
2006	4.908
2007	4.911
2008	4.915