Year	mmol per litre
1980	4.545
1981	4.525
1982	4.506
1983	4.486
1984	4.466
1985	4.444
1986	4.424
1987	4.404
1988	4.385
1989	4.368
1990	4.352
1991	4.335
1992	4.316
1993	4.302
1994	4.287
1995	4.273
1996	4.262
1997	4.253
1998	4.233
1999	4.216
2000	4.204
2001	4.189
2002	4.17
2003	4.151
2004	4.133
2005	4.115
2006	4.097
2007	4.08
2008	4.063