Year	mmol per litre
1980	4.138
1981	4.126
1982	4.115
1983	4.101
1984	4.095
1985	4.091
1986	4.088
1987	4.084
1988	4.08
1989	4.078
1990	4.075
1991	4.073
1992	4.075
1993	4.087
1994	4.101
1995	4.114
1996	4.129
1997	4.145
1998	4.159
1999	4.169
2000	4.17
2001	4.169
2002	4.166
2003	4.159
2004	4.15
2005	4.141
2006	4.131
2007	4.123
2008	4.114