Year	mmol per litre
1980	4.559
1981	4.544
1982	4.527
1983	4.509
1984	4.49
1985	4.469
1986	4.449
1987	4.429
1988	4.408
1989	4.387
1990	4.366
1991	4.346
1992	4.328
1993	4.314
1994	4.3
1995	4.29
1996	4.282
1997	4.276
1998	4.271
1999	4.268
2000	4.266
2001	4.264
2002	4.261
2003	4.26
2004	4.26
2005	4.26
2006	4.261
2007	4.264
2008	4.267