Year	mmol per litre
1980	5.471
1981	5.463
1982	5.45
1983	5.434
1984	5.415
1985	5.396
1986	5.375
1987	5.357
1988	5.343
1989	5.333
1990	5.324
1991	5.316
1992	5.311
1993	5.307
1994	5.304
1995	5.299
1996	5.292
1997	5.286
1998	5.279
1999	5.276
2000	5.27
2001	5.264
2002	5.256
2003	5.244
2004	5.229
2005	5.216
2006	5.204
2007	5.194
2008	5.182