Year	mmol per litre
1980	5.603
1981	5.584
1982	5.564
1983	5.541
1984	5.523
1985	5.5
1986	5.481
1987	5.459
1988	5.432
1989	5.41
1990	5.382
1991	5.367
1992	5.356
1993	5.36
1994	5.371
1995	5.376
1996	5.376
1997	5.374
1998	5.363
1999	5.346
2000	5.325
2001	5.302
2002	5.275
2003	5.25
2004	5.23
2005	5.216
2006	5.193
2007	5.177
2008	5.161