Year	mmol per litre
1980	4.474
1981	4.465
1982	4.459
1983	4.447
1984	4.438
1985	4.43
1986	4.422
1987	4.41
1988	4.397
1989	4.383
1990	4.371
1991	4.359
1992	4.347
1993	4.336
1994	4.325
1995	4.313
1996	4.305
1997	4.295
1998	4.286
1999	4.276
2000	4.267
2001	4.257
2002	4.245
2003	4.23
2004	4.213
2005	4.197
2006	4.18
2007	4.164
2008	4.15