Year	mmol per litre
1980	4.786
1981	4.778
1982	4.768
1983	4.758
1984	4.747
1985	4.737
1986	4.726
1987	4.72
1988	4.715
1989	4.713
1990	4.713
1991	4.715
1992	4.723
1993	4.731
1994	4.743
1995	4.754
1996	4.764
1997	4.774
1998	4.785
1999	4.795
2000	4.807
2001	4.819
2002	4.83
2003	4.838
2004	4.845
2005	4.852
2006	4.859
2007	4.865
2008	4.872