These interval timers were common in radiology departments for many years. Before automatic processing of xray film cassettes, the technician had to manually remove each film, place in various chemical baths for developing. Each step had a certain duration, and this timer was for that purpose. Made in March 1954, the crystal has become a bit yellowed, otherwise the dial with white markings against a black background helped with darkroom reading. Low frequency, low energy light toward the red end of the spectrum could be used in the darkroom; the higher energies of 'white light' would expose and ruin the xray film. The back has some wear, but the front and sides of the case look remarkably clean considering the working chemical enviroment of a radiology darkroom. Powered by winding the key, and set with the metal lever. The alarm is very loud. Many more photos below including 3 of the movement. Runs well, seems to keep time.
Crystal, like flexible celluloid. The setting knob goes through the grommet.
With crystal removed.
Alarm hammers the copper bell very loudly, to alert even the sleepiest of midnight shift xray technicians.