Year	mmol per litre
1980	5.346
1981	5.351
1982	5.355
1983	5.358
1984	5.362
1985	5.364
1986	5.364
1987	5.362
1988	5.36
1989	5.356
1990	5.341
1991	5.322
1992	5.301
1993	5.281
1994	5.257
1995	5.236
1996	5.211
1997	5.185
1998	5.165
1999	5.145
2000	5.129
2001	5.114
2002	5.096
2003	5.078
2004	5.066
2005	5.056
2006	5.051
2007	5.046
2008	5.042