Year	mmol per litre
1980	5.511
1981	5.493
1982	5.477
1983	5.457
1984	5.437
1985	5.413
1986	5.386
1987	5.366
1988	5.345
1989	5.319
1990	5.298
1991	5.282
1992	5.262
1993	5.243
1994	5.233
1995	5.221
1996	5.212
1997	5.198
1998	5.188
1999	5.184
2000	5.176
2001	5.164
2002	5.154
2003	5.143
2004	5.138
2005	5.129
2006	5.127
2007	5.129
2008	5.129