Year	mmol per litre
1980	4.414
1981	4.404
1982	4.394
1983	4.385
1984	4.378
1985	4.373
1986	4.37
1987	4.367
1988	4.365
1989	4.364
1990	4.367
1991	4.369
1992	4.374
1993	4.38
1994	4.386
1995	4.393
1996	4.4
1997	4.412
1998	4.426
1999	4.424
2000	4.423
2001	4.425
2002	4.422
2003	4.42
2004	4.414
2005	4.409
2006	4.402
2007	4.399
2008	4.401