Making sense of watch data.

The heart rate sensor needs direct skin contact

Most watches measure your pulse optically through the skin. Apple writes that the sensors only work on the top of the wrist and that the heart rate sensor should have direct skin contact. In cold conditions, blood flow in the skin of the wrist can be so low that the sensor records no values.

If wrist detection is turned off, Apple Watch does not record background heart rate readings, for example during rest and walking periods. Missing resting heart rate values can therefore have a technical cause.

Several apps can supply the same value

Apple Health and Health Connect collect values from many apps. If your phone and your watch both record steps, there are two sources for the same day. Health Connect resolves such overlaps using the app priority you set yourself.

How to choose sources and grant permissions is explained in the guides on Apple Health and Health Connect.

Manufacturers calculate differently

For HRV, Apple Health stores the value as SDNN. Health Connect has its own data type for this using the RMSSD method. Both numbers are called HRV and are given in milliseconds, but they are not the same. Sleep stages also have different names depending on the manufacturer.

After switching devices, your history can therefore jump even though nothing changed in your everyday life. mypacing shows where the values come from below every chart in your history. If the HRV method changes within the selected period, the app points out that values before and after that day are not directly comparable.

Steps depend on which device you carry

Your phone and your watch count steps independently. If the phone sits on your desk, it counts nothing during that time, while the watch on your wrist does. The daily total therefore depends on which device you carry when, and which source has priority.

In mypacing, steps appear in your history as steps per day and in the weekly view as a weekly average. The daily picture does not show them. It shows resting heart rate, HRV and sleep.

Comparing with yourself stays fair

If device, source and fit stay the same, you measure under similar conditions every day. Your history then mainly shows how your values move. That is why mypacing compares every value with your usual range over the last four weeks and not with reference tables.

After switching devices, this range forms again with the new values. That takes a few weeks.

Sources

All information on this page is based on legal texts, public authorities and manufacturers’ documentation. Most sources are in German. The description of mypacing features reflects the app as of 20 October 2026.

• Möglichst genaue Messwerte mit deiner Apple Watch erhalten, Apple Support. Accessed 20 October 2026.
• Health Connect-Probleme beheben und Feedback geben, Android-Hilfe. Accessed 20 October 2026.
• Schritte mit Health Connect aufzeichnen, Android-Hilfe. Accessed 20 October 2026.
• heartRateVariabilitySDNN (HealthKit), Apple Developer. Accessed 20 October 2026.
• HeartRateVariabilityRmssdRecord (Health Connect), Android Developers. Accessed 20 October 2026.

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