I read that despite the simple measurement mechanism ("shine a light through a finger"), the accuracy is generally pretty high (+/- 2%). This document from the

I read that despite the simple measurement mechanism ("shine a light through a finger"), the accuracy is generally pretty high (+/- 2%). This document from the American Thoracic Society does state some corner cases though [1]. Quote: "How accurate is the pulse oximeter? The oxygen level from a pulse oximeter is reasonably accurate. Most oximeters give a reading 2% over or 2% under what your saturation would be if obtained by an arterial blood gas. For example, if your oxygen saturation reads 92% on the pulse oximeter, it may be actually anywhere from 90 to 94%. The oximeter reading may be less accurate if a person is wearing nail polish, artificial nails, has cold hands, or has poor circulation." [1] https://www.thoracic.org/patients/patient-resources/resources/pulse-oximetry.pdf https://www.thoracic.org/patients/patient-resources/resource...