Year	mmol per litre
1980	5.162
1981	5.147
1982	5.13
1983	5.116
1984	5.101
1985	5.085
1986	5.069
1987	5.048
1988	5.027
1989	4.999
1990	4.967
1991	4.928
1992	4.875
1993	4.817
1994	4.755
1995	4.694
1996	4.629
1997	4.57
1998	4.518
1999	4.473
2000	4.435
2001	4.408
2002	4.386
2003	4.368
2004	4.355
2005	4.346
2006	4.336
2007	4.328
2008	4.32