Year	mmol per litre
1980	5.374
1981	5.374
1982	5.366
1983	5.353
1984	5.338
1985	5.321
1986	5.305
1987	5.288
1988	5.27
1989	5.251
1990	5.234
1991	5.223
1992	5.209
1993	5.191
1994	5.174
1995	5.156
1996	5.138
1997	5.118
1998	5.095
1999	5.073
2000	5.049
2001	5.022
2002	4.992
2003	4.964
2004	4.938
2005	4.912
2006	4.886
2007	4.863
2008	4.84