My heart rate is shown differently across apps

Cardiogram can receive heart rate values from different sources, such as Apple Watch, Fitbit, Garmin, and Wear OS. Except for Apple Health, for most data, Fitbit, Garmin, and WearOS use different algorithms to display your data set in the app so that you may see different variances in BPM between each app.

While we try to display all measurements and display them as clearly as possible, to achieve this, the timeline either averages all heart rate measurements taken within one-minute intervals or displays the highest value recorded during that interval.

When your device is in continuous mode or during activities where measurement frequency increases (often down to the second), these multiple measurements are averaged into a single one-minute value. As a result, while you might notice brief spikes in your heart rate during a workout due to the increased sampling frequency, the timeline will display the average BPM of all measurements taken in that one-minute segment. This ensures a more concise and consistent view of your heart rate data.

Apps such as Fitbit or Garmin Connect often show a summarized view and may leave out high or low values.

An example daily overview is shown in Cardiogram:

This may look different than the daily heart rate graphs shown in the Apple Health app, Fitbit, Garmin, or Google Fit app, which show a summarized view:

In the Fitbit example above, high peak values such as 171 during the Bike ride are not shown in the summarized daily overview because that high heart rate value was only sustained for a few seconds.

It may be possible to view those high values by clicking on the detailed view of the workout:

For Garmin devices, we found that Garmin also uses an average to display your daily overall BPM measurements down to two-minute intervals. You may see a higher heart rate during your workout, but you will not always see that exact measurement in your daily overview. You can read more about this here -> Why Do I See Two Different High Heart Rate Values in Garmin Connect?