Year	mmol per litre
1980	4.401
1981	4.397
1982	4.395
1983	4.39
1984	4.389
1985	4.385
1986	4.382
1987	4.383
1988	4.386
1989	4.387
1990	4.39
1991	4.389
1992	4.385
1993	4.379
1994	4.37
1995	4.361
1996	4.352
1997	4.343
1998	4.332
1999	4.325
2000	4.316
2001	4.312
2002	4.307
2003	4.306
2004	4.305
2005	4.305
2006	4.306
2007	4.31
2008	4.313