Year	mmol per litre
1980	4.656
1981	4.64
1982	4.626
1983	4.608
1984	4.591
1985	4.573
1986	4.557
1987	4.544
1988	4.531
1989	4.519
1990	4.508
1991	4.496
1992	4.482
1993	4.47
1994	4.454
1995	4.44
1996	4.428
1997	4.414
1998	4.402
1999	4.392
2000	4.381
2001	4.371
2002	4.362
2003	4.355
2004	4.348
2005	4.342
2006	4.336
2007	4.331
2008	4.326