Year	mmol per litre
1980	4.661
1981	4.628
1982	4.593
1983	4.556
1984	4.516
1985	4.477
1986	4.437
1987	4.399
1988	4.363
1989	4.329
1990	4.297
1991	4.268
1992	4.24
1993	4.215
1994	4.191
1995	4.17
1996	4.153
1997	4.141
1998	4.131
1999	4.122
2000	4.116
2001	4.113
2002	4.11
2003	4.111
2004	4.112
2005	4.114
2006	4.116
2007	4.119
2008	4.122