I noticed that Intervals almost always records a lower average heart rate than both Strava and Garmin connect. It varies between 3 - 5 HR lower. Is there a reason for that? Which is more accurate?
I just had a look at one of mine and Intervals.icu and Garmin Connect are the same, Strava 1 bpm higher. Could you please post an example activity and I will investigate. Tx.
Herewith a screenshot of an exercise 29 May 2021
where the HR differs - (Strava HR 144), (Intervals HR 141).
All I can think of is that it is something in the way Intervals.icu deals with dropouts (there are a few in that ride, the straight lines on the chart) or interpolation. It interpolates the HR data to 1 second per point ticks, filling in gaps between points and short drop outs with interpolation.
Your device is recording with option 12 or 13 seconds between ticks. You could try set it to record every second and might get more consistent results.