Here are photos of a circa-1944 Perfex Series 155 Magic Dial Thermostat, as well as the instruction manual.
Hoffman Data Book for Heating Engineers and Contractors (1925)
Here is the Hoffman Data Book for Heating Engineers and Contractors, Second Edition compiled for the Hoffman Specialty Company in 1925. "The Hoffman devices which transform what would be an ordinary steam heating system into Hoffman controlled heat are six in number: the control valve (No. 7 Hoffman modulating valve), the trap (No. 8 Hoffman return line valve), the vent valve (No. 11 Hoffman vapor vacuum valve), the Hoffman differential loop, the Hoffman damper regulator, and the Hoffman ther-kompo gage. The book also includes tips for figuring heat losses and radiation, the heat transmission of building materials, pipe sizing data, and more.
Thanks to Patrick Linhardt and J.P. Freeley for scanning and sharing this classic book.
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