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E4 data - HR.csv explanation

In the session zip archive, together with the sensor readings csv files, there's also a file called HR.csv and it looks like the example below:



This file contains the average heart rate values computed in spans of 10 seconds. They're not derived from a real-time reading, but are created only after the session is uploaded on the E4 connect, either using memory mode or the E4 Realtime app.
Those values are derived directly from the BVP analysis of the session and the output of this elaboration is structured in the csv file as follows:

  1. Initial timestamp: This UNIX timestamp corresponds to the first sample of the computed heart rate. Please notice that it is 10 seconds after the beginning of the recording, because the algorithm needs the first 10 seconds of the signal for the initialization.
  2. Sampling rate: it is 1 Hz, so the values provided in the file are 1 sec apart from each other.
  3. Values: The HR values begin at the third row and continue in the rest of the rows.

These values are not shown as a graph on the E4 connect since the HR shown in the session view is the instantaneous HR derived from the IBI (described in our article How is IBI.csv obtained?) and shouldn't be compared with those values.



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