Year	mmol per litre
1980	4.476
1981	4.48
1982	4.487
1983	4.492
1984	4.499
1985	4.5
1986	4.495
1987	4.486
1988	4.476
1989	4.465
1990	4.453
1991	4.444
1992	4.434
1993	4.424
1994	4.409
1995	4.396
1996	4.385
1997	4.371
1998	4.362
1999	4.343
2000	4.328
2001	4.314
2002	4.304
2003	4.298
2004	4.296
2005	4.294
2006	4.295
2007	4.296
2008	4.299