Report issued by the U.S. Bureau of Mines on the magnetic base stations located in Minnesota, Michigan, and Wisconsin. The report evaluates the usefulness of the stations for calibration of certain instruments. This report contains tables, graphs, maps, and illustrations.

From Introduction and Summary: "Reports from operating companies showed that 25,715 men worked at coke ovens in 1951, about 6 percent more than were employed in 1950 and, except in 1943, the largest work force since 1930, when 28,139 men were employed. The work time for all employees was 70,190,493 man-hours. The returns indicated an average of 344 work days per man as compared with 341 days in the previous year. Accidents at the ovens resulted in the death of 10 and injury to 768 workers, both of these figures representing fewer injuries than in 1950."