The app and cloud use the guidelines set by the American Heart Association (AHA, more information here).
The blood pressure monitor uses guidelines developed by the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH).
A detailed comparison can be found on this webpage. The following table shows the differences:
Please note: The iHealth MyVitals app and iHealth Cloud follow AHA guidelines because they’re designed for U.S. users, while the blood pressure devices use ESC guidelines since they’re made for international markets. This can cause slight differences in how readings are labeled, but both are accurate—you can follow the guideline your doctor recommends.