Year	mmol per litre
1980	5.348
1981	5.341
1982	5.336
1983	5.332
1984	5.328
1985	5.323
1986	5.322
1987	5.32
1988	5.327
1989	5.328
1990	5.329
1991	5.338
1992	5.348
1993	5.355
1994	5.357
1995	5.364
1996	5.362
1997	5.361
1998	5.363
1999	5.37
2000	5.375
2001	5.383
2002	5.392
2003	5.401
2004	5.411
2005	5.417
2006	5.423
2007	5.428
2008	5.434