Year	mmol per litre
1980	5.264
1981	5.271
1982	5.277
1983	5.282
1984	5.29
1985	5.295
1986	5.296
1987	5.296
1988	5.296
1989	5.294
1990	5.28
1991	5.264
1992	5.245
1993	5.229
1994	5.207
1995	5.187
1996	5.164
1997	5.138
1998	5.119
1999	5.099
2000	5.082
2001	5.067
2002	5.047
2003	5.027
2004	5.015
2005	5.007
2006	5.003
2007	4.998
2008	4.994