Year	mmol per litre
1980	4.646
1981	4.63
1982	4.616
1983	4.599
1984	4.586
1985	4.572
1986	4.559
1987	4.545
1988	4.531
1989	4.517
1990	4.503
1991	4.487
1992	4.467
1993	4.447
1994	4.43
1995	4.414
1996	4.399
1997	4.385
1998	4.372
1999	4.362
2000	4.353
2001	4.344
2002	4.335
2003	4.323
2004	4.31
2005	4.297
2006	4.284
2007	4.272
2008	4.259