United States. Bureau of Labor Statistics. "Handbook of Labor Statistics, 1929 edition : Part 1 : Bulletin of the United States Bureau of Labor Statistics, No. 491,"
Handbook of Labor Statistics
(August 1929).
https://fraser.stlouisfed.org/title/4025/item/493214/content/pdf/bls_0491_1929_pt1, accessed on July 27, 2026.