Sentence:  Direct reading of COHb usually is performed in the clinical or hospital setting through the use of a direct-reading spectrophotometer, such as a CO-<WSD>Oximeter</WSD> (CO-Ox). 
Meaning of the word marked with <WSD> tags:  A device that measures the oxygen saturation of arterial blood. (from 1942)<ref name="Brans & Hay"/>