Year	mmol per litre
1980	4.86
1981	4.861
1982	4.859
1983	4.858
1984	4.857
1985	4.854
1986	4.85
1987	4.849
1988	4.85
1989	4.851
1990	4.857
1991	4.867
1992	4.878
1993	4.891
1994	4.906
1995	4.922
1996	4.936
1997	4.951
1998	4.957
1999	4.958
2000	4.96
2001	4.962
2002	4.963
2003	4.968
2004	4.971
2005	4.973
2006	4.976
2007	4.977
2008	4.98