Year	mmol per litre
1980	4.606
1981	4.601
1982	4.594
1983	4.586
1984	4.572
1985	4.558
1986	4.542
1987	4.528
1988	4.511
1989	4.497
1990	4.482
1991	4.47
1992	4.459
1993	4.45
1994	4.441
1995	4.435
1996	4.425
1997	4.424
1998	4.421
1999	4.421
2000	4.425
2001	4.423
2002	4.418
2003	4.413
2004	4.412
2005	4.41
2006	4.405
2007	4.399
2008	4.397