Year	mmol per litre
1980	4.197
1981	4.196
1982	4.198
1983	4.2
1984	4.205
1985	4.208
1986	4.211
1987	4.214
1988	4.213
1989	4.206
1990	4.195
1991	4.18
1992	4.161
1993	4.141
1994	4.119
1995	4.1
1996	4.083
1997	4.07
1998	4.061
1999	4.055
2000	4.052
2001	4.052
2002	4.053
2003	4.055
2004	4.058
2005	4.059
2006	4.061
2007	4.064
2008	4.066