Year	mmol per litre
1980	4.468
1981	4.454
1982	4.439
1983	4.424
1984	4.409
1985	4.393
1986	4.375
1987	4.357
1988	4.339
1989	4.32
1990	4.299
1991	4.279
1992	4.259
1993	4.239
1994	4.219
1995	4.201
1996	4.186
1997	4.174
1998	4.163
1999	4.153
2000	4.144
2001	4.135
2002	4.127
2003	4.12
2004	4.112
2005	4.103
2006	4.093
2007	4.083
2008	4.074