Don't compare the s9+ with other devices, s9 is one of best phones at every section like camera, display, processor, good and accurate censors, its only lags behind battery..
According to a clinical research and I Quote " There is no evidence that any smartphone technology is accurate for the measurement of blood oxygen saturation for clinical use. Furthermore, the scientific basis of such technologies is questionable. Oxygen saturation levels obtained from such technologies should not be trusted in the clinical assessment of patients"
So yeah here u have it... cannot take it that seriously
The basic funda behind it is blood oxygen level is estimated based on the kind of reflection, so a.) how much light comes back to the sensor b.) WHICH light comes back to the sensor.Oxygenated Hemoglobin (=blood with good oxygen saturation) has a bright red color and absorbs more infrared light.Deoxygenated Hemoglobin (=blood with bad oxygen saturation) has a dark red color and absorbs more red light. So by emitting a large-spectrum light (R and IR) and measuring the ratio of the feedback, the device can make a estimation of the blood oxygen level. and surprisingly it's quite aqurate....with medical instruments I compared once in my hospital only 3or 2 % difference ...we tell that is negligible...because pulse oxymeter allaways have 2% error window where arterial oxygen measurement is aqurate...so for correction we allaways do 3 times then average.... ( Note ...pulse oxymeter = 95 to 100% normal, arterial oxymeter = 75 to 100% normal)
