It seems to work fine, pulse oximeter we have no way of calibrating it against a top notch measuring system. One oddity is the battery compartment – normally the negative (flat) end of a battery goes on a coil spring. In this device the coils are both at the same end and one connects to the positive terminal. It fooled us at first.The new OLED (Organic Light Emitting Diode) technology is phenomenal … like the strip above the keyboard on the new MacBook Pro 15 laptop computer. It is bright, sharp, clear and extremely easy to read in all light conditions. It also costs about 1/3 as much as my earlier top-of-the-line oximeter (which stopped working). The six different selections make it easy to read in any position, and the two high-resolution “wave form” heartbeat line displays of my heart beat is most interesting, helpful and a great added bonus.