A hindcast is a reverse forecast.
All data is "tainted" between 1880 and 2013 because that is what I have been using for a fit. So I need to go backwards from that point. The GISS data only starts at 1880, but the British HadCRUT temperature data goes back further.
It works to 1866, which is where the SOI data starts.
If it is OK to use the tainted range, one can test against training intervals within this range
This is a set of different training intervals that project after the up-arrow