Year	mmol per litre
1980	4.51
1981	4.503
1982	4.497
1983	4.489
1984	4.483
1985	4.481
1986	4.478
1987	4.476
1988	4.473
1989	4.472
1990	4.471
1991	4.468
1992	4.467
1993	4.467
1994	4.466
1995	4.467
1996	4.468
1997	4.469
1998	4.47
1999	4.469
2000	4.47
2001	4.469
2002	4.471
2003	4.473
2004	4.476
2005	4.477
2006	4.481
2007	4.485
2008	4.49