Year	mmol per litre
1980	4.769
1981	4.752
1982	4.735
1983	4.716
1984	4.695
1985	4.676
1986	4.654
1987	4.635
1988	4.618
1989	4.602
1990	4.588
1991	4.575
1992	4.561
1993	4.55
1994	4.535
1995	4.519
1996	4.504
1997	4.493
1998	4.482
1999	4.473
2000	4.465
2001	4.459
2002	4.456
2003	4.453
2004	4.453
2005	4.454
2006	4.455
2007	4.458
2008	4.461