United States. Bureau of Labor Statistics. "Labor Requirements for Construction Materials. Pt. II—Concrete Masonry Units : Bulletin of the United States Bureau of Labor Statistics, No. 888-2" in Labor Requirements for Construction Materials : Bulletin of the United States Bureau of Labor Statistics, No. 888 (1947). https://fraser.stlouisfed.org/title/4343/item/495026, accessed on March 13, 2025.