Year	mmol per litre
1980	4.647
1981	4.634
1982	4.619
1983	4.602
1984	4.586
1985	4.57
1986	4.553
1987	4.535
1988	4.519
1989	4.502
1990	4.486
1991	4.471
1992	4.454
1993	4.439
1994	4.423
1995	4.412
1996	4.402
1997	4.393
1998	4.386
1999	4.381
2000	4.378
2001	4.376
2002	4.374
2003	4.372
2004	4.368
2005	4.365
2006	4.362
2007	4.359
2008	4.356