Year	mmol per litre
1980	4.66
1981	4.663
1982	4.666
1983	4.668
1984	4.67
1985	4.675
1986	4.678
1987	4.685
1988	4.693
1989	4.705
1990	4.721
1991	4.738
1992	4.755
1993	4.775
1994	4.795
1995	4.815
1996	4.835
1997	4.852
1998	4.86
1999	4.868
2000	4.878
2001	4.888
2002	4.899
2003	4.913
2004	4.926
2005	4.939
2006	4.956
2007	4.974
2008	4.993