Year	mmol per litre
1980	4.52
1981	4.495
1982	4.472
1983	4.449
1984	4.428
1985	4.408
1986	4.389
1987	4.37
1988	4.354
1989	4.339
1990	4.327
1991	4.317
1992	4.309
1993	4.304
1994	4.3
1995	4.297
1996	4.298
1997	4.298
1998	4.296
1999	4.295
2000	4.294
2001	4.292
2002	4.289
2003	4.286
2004	4.284
2005	4.282
2006	4.282
2007	4.283
2008	4.284