The RED line indicates the average annualized adjustments from data posted in March 2007,
the BLUE line indicates the average annualized adjustments from data posted in January 2005.
The line indicates differences (subtracting averages of earlier adjustments from those of recent adjustments).
When the line is positive, the recent adjustments are more positive/less negative than the earlier adjustments;
when the line is negative, the recent adjustments are more negative/less positive than the earlier adjustments.
1909 is the first year for which the USHCN included annual adjusted averages for at least 1000 stations.