Year	mmol per litre
1980	4.352
1981	4.328
1982	4.312
1983	4.299
1984	4.28
1985	4.257
1986	4.238
1987	4.228
1988	4.217
1989	4.206
1990	4.195
1991	4.182
1992	4.17
1993	4.154
1994	4.141
1995	4.128
1996	4.118
1997	4.11
1998	4.103
1999	4.096
2000	4.093
2001	4.091
2002	4.089
2003	4.087
2004	4.085
2005	4.083
2006	4.081
2007	4.078
2008	4.076