Year	mmol per litre
1980	4.592
1981	4.585
1982	4.575
1983	4.56
1984	4.546
1985	4.532
1986	4.516
1987	4.503
1988	4.489
1989	4.476
1990	4.464
1991	4.453
1992	4.444
1993	4.435
1994	4.425
1995	4.416
1996	4.409
1997	4.402
1998	4.397
1999	4.388
2000	4.38
2001	4.372
2002	4.361
2003	4.351
2004	4.34
2005	4.331
2006	4.322
2007	4.315
2008	4.308