Year	mmol per litre
1980	4.487
1981	4.479
1982	4.471
1983	4.463
1984	4.456
1985	4.449
1986	4.442
1987	4.434
1988	4.426
1989	4.42
1990	4.412
1991	4.405
1992	4.398
1993	4.393
1994	4.387
1995	4.38
1996	4.373
1997	4.367
1998	4.359
1999	4.348
2000	4.338
2001	4.327
2002	4.316
2003	4.305
2004	4.294
2005	4.283
2006	4.273
2007	4.262
2008	4.252