Year	mmol per litre
1980	5.41
1981	5.406
1982	5.4
1983	5.393
1984	5.387
1985	5.379
1986	5.373
1987	5.365
1988	5.362
1989	5.358
1990	5.352
1991	5.342
1992	5.33
1993	5.318
1994	5.301
1995	5.287
1996	5.272
1997	5.263
1998	5.25
1999	5.234
2000	5.213
2001	5.193
2002	5.177
2003	5.158
2004	5.136
2005	5.121
2006	5.11
2007	5.102
2008	5.095