Year	mmol per litre
1980	4.632
1981	4.617
1982	4.601
1983	4.582
1984	4.562
1985	4.538
1986	4.517
1987	4.5
1988	4.486
1989	4.475
1990	4.465
1991	4.456
1992	4.446
1993	4.437
1994	4.43
1995	4.421
1996	4.411
1997	4.403
1998	4.398
1999	4.393
2000	4.388
2001	4.387
2002	4.386
2003	4.384
2004	4.383
2005	4.381
2006	4.378
2007	4.376
2008	4.373