A pulse oximeter measures two things: pulse and oxygen saturation level. The pulse rate is a measure of how fast your heart is beating, and it is measured in beats per minute (bpm) . The oxygen saturation level is a measure of how much oxygen is in your blood, and it is presented as a percentage. The two main numbers displayed on a pulse oximeter are the oxygen saturation level and the pulse rate. The oxygen saturation level is abbreviated as SpO2 (peripheral oxygen saturation) and is usually between 95% and 100% for most healthy individuals. A healthy heart rate is between 50 and 90 bpm. It is important to note that pulse oximeters have limitations and a risk of inaccuracy under certain circumstances.