Year	mmol per litre
1980	5.613
1981	5.588
1982	5.56
1983	5.532
1984	5.505
1985	5.476
1986	5.45
1987	5.421
1988	5.395
1989	5.368
1990	5.341
1991	5.31
1992	5.274
1993	5.24
1994	5.201
1995	5.161
1996	5.116
1997	5.075
1998	5.036
1999	5.008
2000	4.98
2001	4.959
2002	4.943
2003	4.934
2004	4.929
2005	4.926
2006	4.925
2007	4.925
2008	4.926