Year	mmol per litre
1980	5.55
1981	5.536
1982	5.518
1983	5.499
1984	5.477
1985	5.455
1986	5.434
1987	5.415
1988	5.399
1989	5.386
1990	5.374
1991	5.362
1992	5.351
1993	5.342
1994	5.332
1995	5.321
1996	5.309
1997	5.296
1998	5.284
1999	5.274
2000	5.261
2001	5.25
2002	5.237
2003	5.223
2004	5.206
2005	5.192
2006	5.18
2007	5.171
2008	5.161