Year	mmol per litre
1980	4.376
1981	4.36
1982	4.348
1983	4.338
1984	4.33
1985	4.325
1986	4.32
1987	4.311
1988	4.305
1989	4.3
1990	4.292
1991	4.285
1992	4.279
1993	4.274
1994	4.27
1995	4.267
1996	4.268
1997	4.27
1998	4.272
1999	4.276
2000	4.282
2001	4.291
2002	4.299
2003	4.306
2004	4.315
2005	4.327
2006	4.338
2007	4.35
2008	4.362