Year	mmol per litre
1980	4.654
1981	4.638
1982	4.623
1983	4.61
1984	4.597
1985	4.584
1986	4.572
1987	4.56
1988	4.549
1989	4.538
1990	4.526
1991	4.514
1992	4.501
1993	4.49
1994	4.478
1995	4.467
1996	4.454
1997	4.442
1998	4.43
1999	4.418
2000	4.404
2001	4.391
2002	4.38
2003	4.369
2004	4.361
2005	4.352
2006	4.342
2007	4.331
2008	4.322