Year	mmol per litre
1980	5.46
1981	5.455
1982	5.448
1983	5.44
1984	5.434
1985	5.426
1986	5.417
1987	5.409
1988	5.402
1989	5.395
1990	5.388
1991	5.375
1992	5.36
1993	5.354
1994	5.349
1995	5.342
1996	5.334
1997	5.329
1998	5.318
1999	5.306
2000	5.295
2001	5.287
2002	5.275
2003	5.262
2004	5.247
2005	5.232
2006	5.219
2007	5.208
2008	5.196