Year	mmol per litre
1980	4.738
1981	4.725
1982	4.716
1983	4.705
1984	4.693
1985	4.681
1986	4.668
1987	4.655
1988	4.642
1989	4.629
1990	4.613
1991	4.598
1992	4.58
1993	4.566
1994	4.544
1995	4.52
1996	4.494
1997	4.469
1998	4.449
1999	4.433
2000	4.422
2001	4.414
2002	4.409
2003	4.407
2004	4.407
2005	4.407
2006	4.408
2007	4.41
2008	4.412