Year	mmol per litre
1980	4.751
1981	4.714
1982	4.681
1983	4.648
1984	4.618
1985	4.593
1986	4.572
1987	4.553
1988	4.544
1989	4.536
1990	4.527
1991	4.519
1992	4.51
1993	4.502
1994	4.497
1995	4.492
1996	4.49
1997	4.49
1998	4.495
1999	4.505
2000	4.512
2001	4.52
2002	4.527
2003	4.531
2004	4.533
2005	4.533
2006	4.532
2007	4.529
2008	4.525