Series Is Presented Here As Two Variables--(1)-- Original Data, 1913-1922 (2)--Original Data, 1921-1939. Prices Are For United States, Average, All Grades. Ratio Of 1921 For Overlap: 7.72 Divided By 8.84 Equals 87.3%. Source: Sent Directly From Bls
This NBER data series m04144a appears on the NBER website in Chapter 4 at http://www.nber.org/databases/macrohistory/contents/chapter04.html.
NBER Indicator: m04144a
Release: NBER Macrohistory Database
National Bureau of Economic Research, Wholesale Price of By-Product Coke for United States [M0444AUSM294NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M0444AUSM294NNBR, May 5, 2016.