1. Take a small silent breath in and a small silent breath out. Start the stopwatch above.
2. Pinch your nose with your fingers to prevent air from entering into your lungs.
3. Hold your breath until your first urge to breathe or until you feel your chest or diaphragm (belly) involuntarily moving, whichever comes first.
4. When this happens, stop the stopwatch, release your nose and breathe in through it normally, avoid taking a deep breath in.
Note: Your inhalation after the breath-hold should be no larger than your breath prior to taking the measurement. It should be calm and quiet.