Year	mmol per litre
1980	4.428
1981	4.414
1982	4.404
1983	4.389
1984	4.373
1985	4.358
1986	4.347
1987	4.338
1988	4.331
1989	4.323
1990	4.318
1991	4.311
1992	4.301
1993	4.294
1994	4.28
1995	4.269
1996	4.261
1997	4.25
1998	4.24
1999	4.234
2000	4.227
2001	4.224
2002	4.22
2003	4.219
2004	4.221
2005	4.22
2006	4.222
2007	4.221
2008	4.222