Year	mmol per litre
1980	4.712
1981	4.694
1982	4.682
1983	4.666
1984	4.644
1985	4.626
1986	4.606
1987	4.586
1988	4.567
1989	4.547
1990	4.526
1991	4.505
1992	4.482
1993	4.46
1994	4.439
1995	4.42
1996	4.402
1997	4.383
1998	4.364
1999	4.345
2000	4.325
2001	4.305
2002	4.285
2003	4.265
2004	4.245
2005	4.225
2006	4.206
2007	4.187
2008	4.169