@drrob99 This is unfortunately true in many cases, and it's often 'operator error.' Not for an instant wanting to sound like a victim blamer, I only mean that if one can be sure of one's use of an implement it can often point to mistakes that can be corrected, thus vastly increasing the implement's true utility. Over at afibbers.org we see posts by people who report initially ambiguous or apparently wrong results from a watch or Kardia, only to go on to say they learned more, practiced, and now have more consistent and apparently correct reports from those devices. A Kardia, for example, needs to have clean hands and touch pads, and good contact on both contact pads. But what tekkie50 said makes a lot of sense...three posts back. Have at least two devices that you can use AT THE SAME TIME, or right after one another, so that they both get to sample the cardiac behaviour of interest. From there, you can compare those reports to find commonality, yes, hopefully, but also to help build your confidence and experience so that if you only have one handy you know you can count on it for a veridical assessment.