Year	mmol per litre
1980	5.63
1981	5.611
1982	5.589
1983	5.572
1984	5.555
1985	5.541
1986	5.527
1987	5.509
1988	5.493
1989	5.476
1990	5.459
1991	5.441
1992	5.424
1993	5.408
1994	5.392
1995	5.376
1996	5.358
1997	5.339
1998	5.322
1999	5.304
2000	5.283
2001	5.259
2002	5.235
2003	5.21
2004	5.183
2005	5.157
2006	5.131
2007	5.101
2008	5.071