Before you start your practise, place the pulse oximeter on your finger, as per your device instructions. Your device instructions will tell you clearly what each reading on your screen means.
You can use your pulse oximeter to watch your pulse increase and decrease with your inhale and exhale. Your pulse oximeter gives you an estimated measure of your blood SpO₂ levels.
At the beginning of the session, the SpO₂ reading should be around 95% or higher. This is a normal SpO₂ saturation.
When you hold your breath after exhaling fully, you will see that percentage start to drop slowly. When your SpO₂ level reads at 85% or less, it means you are in hypoxia. Aim to continue holding your breath for at least 30 seconds beyond this. Ideally, you will eventually be able to hold your breath for 1-2 minutes at 85% or lower.
The pulse oximeter can be distracting, so once you see the “evidence” that you can do this, you can forget about the oximeter and simply focus on your meditation.