When I choose the Pulse Oximeter widget, the display alternates between "MEASURING" and "KEEP STILL". The red "progress" bar around the edge usually advances half way and then stalls. After about a minute the message, "Unable to take a measurement. Sit comfortably..." appears. Per the user's manual, I am motionless, wearing the device snugly above my wrist bone, holding the device near heart level, have a clean and dry arm, etc. FWIW, I do have a low resting heart rate (~39 bpm).