Year	mmol per litre
1980	5.518
1981	5.507
1982	5.498
1983	5.487
1984	5.475
1985	5.463
1986	5.45
1987	5.437
1988	5.428
1989	5.417
1990	5.407
1991	5.397
1992	5.382
1993	5.364
1994	5.34
1995	5.31
1996	5.285
1997	5.26
1998	5.239
1999	5.215
2000	5.191
2001	5.169
2002	5.148
2003	5.129
2004	5.111
2005	5.1
2006	5.09
2007	5.081
2008	5.073