Year	mmol per litre
1980	5.504
1981	5.509
1982	5.508
1983	5.499
1984	5.481
1985	5.459
1986	5.432
1987	5.407
1988	5.382
1989	5.362
1990	5.337
1991	5.317
1992	5.3
1993	5.29
1994	5.283
1995	5.282
1996	5.281
1997	5.282
1998	5.285
1999	5.288
2000	5.291
2001	5.288
2002	5.283
2003	5.275
2004	5.269
2005	5.269
2006	5.262
2007	5.257
2008	5.251