I have a cheap one so I am not sure if the absolute values are correct. But they change very reliably and consistently. With breathing exercises I can take the

I have a cheap one so I am not sure if the absolute values are correct. But they change very reliably and consistently. With breathing exercises I can take the value from the usual 95-97 to 99. When I hold my breath long enough I can take the value down to 75 or less. There is a delay of 20-30 seconds between changing my breathing to the oximeter changing its value. I suppose this is how long it takes for the blood to get around in the body.