Year	mmol per litre
1980	4.889
1981	4.887
1982	4.882
1983	4.875
1984	4.868
1985	4.86
1986	4.851
1987	4.837
1988	4.818
1989	4.797
1990	4.785
1991	4.778
1992	4.768
1993	4.76
1994	4.748
1995	4.744
1996	4.743
1997	4.74
1998	4.737
1999	4.725
2000	4.715
2001	4.705
2002	4.694
2003	4.688
2004	4.681
2005	4.673
2006	4.669
2007	4.668
2008	4.667