Year	mmol per litre
1980	5.559
1981	5.532
1982	5.506
1983	5.48
1984	5.454
1985	5.429
1986	5.404
1987	5.376
1988	5.345
1989	5.316
1990	5.286
1991	5.253
1992	5.222
1993	5.191
1994	5.161
1995	5.132
1996	5.102
1997	5.075
1998	5.053
1999	5.03
2000	5.009
2001	4.989
2002	4.97
2003	4.957
2004	4.945
2005	4.937
2006	4.933
2007	4.93
2008	4.928