guides.

Plain answers about stress, HRV and your Apple Watch. Every guide cites its sources.

• Can Apple Watch measure cortisol?

  No watch can read cortisol. Here is what Apple Watch actually measures, how those signals relate to stress, and how cortisol is really tested.

• How to check your HRV on Apple Watch

  Where to find heart rate variability on iPhone and Apple Watch, what the number means, and why comparing it with your own normal matters more than any "good" value.