Year	mmol per litre
1980	4.535
1981	4.525
1982	4.519
1983	4.508
1984	4.499
1985	4.491
1986	4.483
1987	4.472
1988	4.46
1989	4.448
1990	4.438
1991	4.428
1992	4.418
1993	4.41
1994	4.401
1995	4.393
1996	4.385
1997	4.378
1998	4.37
1999	4.364
2000	4.358
2001	4.351
2002	4.343
2003	4.332
2004	4.319
2005	4.305
2006	4.292
2007	4.28
2008	4.268