Year	mmol per litre
1980	4.7
1981	4.679
1982	4.662
1983	4.647
1984	4.626
1985	4.603
1986	4.583
1987	4.568
1988	4.553
1989	4.537
1990	4.52
1991	4.503
1992	4.487
1993	4.468
1994	4.449
1995	4.431
1996	4.414
1997	4.398
1998	4.384
1999	4.37
2000	4.357
2001	4.345
2002	4.331
2003	4.316
2004	4.301
2005	4.286
2006	4.269
2007	4.252
2008	4.236