Antique Improved "Robertson-Thompson instrument manufactured by James L. Robertson & Sons of New York City #7540. It may have been used to calibrate various "bourdon tube" pressure gauges or more likely to test steam pressure on the Union Pacific Railroad but i cant say for sure.The papers date from the 1920s up into the 1940s.Its in a walnut case that measures 7" x 10" x 11".
Price $ 195

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