Checking historical data

Shiller's Historical inflation

How does one come up with very old data? Use historical newspapers and other reported indexes at the time. Data collected in 1890 had greater error than data collected in 1925, because of increased technology. Or, more plainly, how did Shiller filter for local (temporarl) volatility? We must to deduce anything in the variance change.

Political calculates that the change in volatility from 1890 to 1925 as follows:

"We find, through simple visual inspection, that the Federal Reserve has indeed had a powerful effect upon the volatility we observe in the rate of inflation in the United States."

The problem is that a lot of industries had lower inventory volatility by using newer technology.