Most pulse oximeters are accurate to within 2% to 4% of the actual blood oxygen saturation level. This means that a pulse oximeter reading may be anywhere from 2% to 4% higher or lower than the actual oxygen level in arterial blood. A number of factors can impair the functioning or accuracy of a pulse oximeter.
Fact Sheets > Yale Medicine” >https://www.yalemedicine.org/conditions/pulse-oximetry
