Year	mmol per litre
1980	5.547
1981	5.536
1982	5.525
1983	5.515
1984	5.504
1985	5.489
1986	5.477
1987	5.462
1988	5.446
1989	5.428
1990	5.407
1991	5.38
1992	5.348
1993	5.309
1994	5.263
1995	5.219
1996	5.171
1997	5.126
1998	5.083
1999	5.043
2000	5.007
2001	4.976
2002	4.95
2003	4.929
2004	4.915
2005	4.904
2006	4.895
2007	4.889
2008	4.883