PROBLEM TO BE SOLVED: To provide a robust and wearable device acquiring effective data desired therefor and having improved convenience and comfort for patients.SOLUTION: A method for measuring oxygen saturation of an individual is disclosed, the method including: a measuring step of measuring an electrocardiogram signal over multiple heart beats； a measuring step of measuring one or more pulse oximetry signals over multiple heat beats such that the electrocardiogram signal and the one or more pulse oximetry signals are in time concordance over the one or more heart beats； a comparison step of comparing a portion of the electrocardiogram signal and the one or more pulse oximetry signals in time concordance over the one or more heart beats to detect a constant and a primary periodic component of each of the one or more pulse oximetry signals； and a determination step of determining oxygen saturation from the constant components and primary periodic components from the one or more oximetry signals.SELECTED DRAWING: Figure 6C
