The brochure describes the operation, application, and specifications of a system designed to monitor oxygen partial pressure in pilots' masks and helmets and warn them when levels dip dangerously low.
Beckman Instruments. “Hypoxia Warning System for Monitoring Partial Pressure of Oxygen in Artificial Atmospheric Environments,” circa 1963. Beckman Historical Collection, Box 16, Folder 12. Science History Institute. Philadelphia. https://digital.sciencehistory.org/works/kd17ct42v.