Year	mmol per litre
1980	5.389
1981	5.373
1982	5.359
1983	5.343
1984	5.328
1985	5.313
1986	5.298
1987	5.28
1988	5.264
1989	5.246
1990	5.227
1991	5.206
1992	5.182
1993	5.149
1994	5.112
1995	5.071
1996	5.033
1997	5.001
1998	4.978
1999	4.962
2000	4.949
2001	4.938
2002	4.93
2003	4.925
2004	4.924
2005	4.925
2006	4.925
2007	4.928
2008	4.928