Year	mmol per litre
1980	5.243
1981	5.239
1982	5.231
1983	5.22
1984	5.21
1985	5.203
1986	5.189
1987	5.172
1988	5.155
1989	5.137
1990	5.114
1991	5.093
1992	5.076
1993	5.063
1994	5.047
1995	5.033
1996	5.019
1997	5.008
1998	5
1999	4.988
2000	4.974
2001	4.961
2002	4.942
2003	4.928
2004	4.919
2005	4.91
2006	4.904
2007	4.9
2008	4.896