Byer, Herman B. , United States. Bureau of Labor Statistics and United States. Works Progress Administration. "West North Central Cities, Volume IV" in Salaries and Hours of Labor in Municipal Fire Departments, July 1, 1938 : Bulletin of the United States Bureau of Labor Statistics, No. 684 (1941). https://fraser.stlouisfed.org/scribd/?item_id=494405&filepath=/files/docs/publications/bls/bls_0684-v4_1941.pdf&start_page=1, accessed on October 20, 2017.