Occupational Outlook Handbook, 1970-71 edition : Part 4 : Bulletin of the United States Bureau of Labor Statistics, No. 1650
United States. Bureau of Labor Statistics. "Occupational Outlook Handbook, 1970-71 edition : Part 4 : Bulletin of the United States Bureau of Labor Statistics, No. 1650," Occupational Outlook Handbook (1970). https://fraser.stlouisfed.org/title/3964/item/499632/content/pdf/bls_1650_1970_pt4, accessed on April 20, 2024.