Year	mmol per litre
1980	4.378
1981	4.372
1982	4.367
1983	4.363
1984	4.359
1985	4.357
1986	4.353
1987	4.347
1988	4.342
1989	4.334
1990	4.325
1991	4.314
1992	4.304
1993	4.295
1994	4.287
1995	4.277
1996	4.267
1997	4.26
1998	4.252
1999	4.244
2000	4.234
2001	4.225
2002	4.217
2003	4.21
2004	4.205
2005	4.199
2006	4.192
2007	4.184
2008	4.178