It is a quick, non-invasive and completely painless test which gives a quick and accurate results within 10 seconds. Make sure you are relaxed, breathing normally and in a seated position. Simply clamp the oximeter onto your ring, middle or index fingertip. Make sure your nail is clean with no fingernail polish as it can obscure the results. The oximeter works best when it is at the same level as your heart. Press the button to deactivate sleep mode, wait for 3 seconds and your heartrate and SpO2 levels should appear on the screen. The oximeter sounds an alarm if your SpO2 levels are below 88% or if your pulse is lower than 40 beats per minute or higher than 120 beats per minute.