This works really well and pretty closely matched ECG waveform and readings. I have used this for more than 6 months and it is very helpful. You have to practice holding the phone with your finger over the camera and light, and when I upgraded iPhones I had to practice again to get used to where the camera lense and lamp were on the new phone. Also I have checked it for accuracy multiple times while connected to an ECG in the hospital emergency department !! It is very close to ECG readings... but obviously just a tool to help you, not a medical device. Thank you to whoever created this.