I had an inogen portable that never gave me enough oxygen. I was coming back from the shopping trip with sore muscles and headache . No matter how you set machines use an Oximeter to check your oxygen level. You will be surprised . If you turn a portable concentrator to its highest setting it will include more outside air to the “pulsed” action . Those settings on it are not ltrs. They are just settings on a knob. No portable oxygen concentrator can pulse deliver more than 3 ltrs. If you need more get a tank with a regulator and be nourished .