Year	mmol per litre
1980	5.555
1981	5.535
1982	5.51
1983	5.482
1984	5.454
1985	5.422
1986	5.391
1987	5.362
1988	5.335
1989	5.313
1990	5.294
1991	5.276
1992	5.263
1993	5.251
1994	5.238
1995	5.228
1996	5.217
1997	5.214
1998	5.214
1999	5.212
2000	5.211
2001	5.206
2002	5.2
2003	5.195
2004	5.191
2005	5.186
2006	5.181
2007	5.176
2008	5.169