Year	mmol per litre
1980	5.55
1981	5.544
1982	5.541
1983	5.539
1984	5.536
1985	5.531
1986	5.529
1987	5.525
1988	5.531
1989	5.529
1990	5.526
1991	5.53
1992	5.534
1993	5.534
1994	5.526
1995	5.525
1996	5.515
1997	5.505
1998	5.497
1999	5.495
2000	5.49
2001	5.49
2002	5.49
2003	5.492
2004	5.495
2005	5.494
2006	5.492
2007	5.49
2008	5.488