Year	mmol per litre
1980	4.389
1981	4.391
1982	4.393
1983	4.395
1984	4.399
1985	4.401
1986	4.404
1987	4.412
1988	4.419
1989	4.425
1990	4.431
1991	4.437
1992	4.442
1993	4.447
1994	4.45
1995	4.454
1996	4.459
1997	4.463
1998	4.467
1999	4.472
2000	4.476
2001	4.48
2002	4.484
2003	4.486
2004	4.488
2005	4.491
2006	4.493
2007	4.497
2008	4.503