I recently met Ryan Diesem on a Sea Puffers cruise.  He tested us oxygen users with an Oxygen Dose Recorder.  It hooks between the cannula and the portable concentrator and measured saturation, heart rate as we moved around, showing whether the portable equipment we were using was adequate for our needs.  I have never seen this device before and wondered if other people have been tested when oxygen is prescribed or a portable concentrator is given out.  It sure seems to be a vital test for anyone using a portable concentrator.  My oxygen company wanted to give me a portable concentrator with no test at all