Year	mmol per litre
1980	4.699
1981	4.69
1982	4.681
1983	4.67
1984	4.653
1985	4.634
1986	4.616
1987	4.601
1988	4.585
1989	4.574
1990	4.561
1991	4.549
1992	4.54
1993	4.533
1994	4.527
1995	4.523
1996	4.519
1997	4.517
1998	4.516
1999	4.514
2000	4.515
2001	4.517
2002	4.521
2003	4.525
2004	4.529
2005	4.533
2006	4.536
2007	4.54
2008	4.543