Fig. 5.

Spectrophotometric oximetry devices from the 1950s. (a), (b) Wood oximeters Waters X-350 and Waters XE-60A for oximetry measurements on the ear. Image courtesy of the Wood Library-Museum of Anesthesiology, Schaumburg, Illinois, United States. (c), (d) Comparison of the Cyclops and Atlas oximeters by measuring in transmission mode at the ear (Atlas; transmission mode) and on the forehead (Cyclops; reflectance mode) on a subject while breathing different ${\mathrm{O}}_2$ concentrations.¹²³ Figures (c) and (d) reprinted and modified from Zijlstra et al.,¹²³ with permission from the publisher. (e) Ear oximeter developed by Nilsson.¹²⁴ Reprinted and modified from Nilsson,¹²⁴ with permission from the publisher.