Year	mmol per litre
1980	5.436
1981	5.43
1982	5.422
1983	5.414
1984	5.406
1985	5.397
1986	5.389
1987	5.382
1988	5.377
1989	5.373
1990	5.368
1991	5.358
1992	5.346
1993	5.343
1994	5.34
1995	5.334
1996	5.323
1997	5.318
1998	5.304
1999	5.291
2000	5.276
2001	5.267
2002	5.252
2003	5.238
2004	5.222
2005	5.207
2006	5.194
2007	5.186
2008	5.176