Year	mmol per litre
1980	5.253
1981	5.246
1982	5.236
1983	5.228
1984	5.22
1985	5.211
1986	5.203
1987	5.193
1988	5.184
1989	5.172
1990	5.156
1991	5.137
1992	5.114
1993	5.089
1994	5.062
1995	5.032
1996	5
1997	4.968
1998	4.938
1999	4.911
2000	4.886
2001	4.866
2002	4.848
2003	4.832
2004	4.819
2005	4.803
2006	4.791
2007	4.779
2008	4.768