I think there's an inconsistency with the title of the article and what's mentioned. The title suggests that the study used 'Cardiogram and Apple watch'. However in the article it says that other wearable were also part of this study:

> Now, the startup is reaching a new milestone, this morning publishing the first large-N peer-reviewed clinical study showing that the Apple Watch and other wearables can detect atrial fibrillation with a high degree of accuracy.