17.5 parts of oxygen recorded inside a mask. You need a minimum of 19.5 to avoid headaches and other ill effects.
Normal read would be 20.5 in air.
Masks deprive you of oxygen even if you are sitting still.
No news channel will tell you. If you are working or running, it will be far worse still. VIDEO.
facebook are saying it’s false but there is a simple on camera reading. You decide.