Year	mmol per litre
1980	4.535
1981	4.531
1982	4.529
1983	4.53
1984	4.539
1985	4.542
1986	4.545
1987	4.547
1988	4.551
1989	4.56
1990	4.577
1991	4.591
1992	4.606
1993	4.614
1994	4.611
1995	4.611
1996	4.608
1997	4.605
1998	4.602
1999	4.594
2000	4.592
2001	4.591
2002	4.589
2003	4.586
2004	4.589
2005	4.594
2006	4.6
2007	4.603
2008	4.605