While the definition and meaning of HRV is well-understood and agreed upon, there’s actually more than one way to measure it. There’s also more than one way to transform that measurement into a single numerical score. Different health and fitness products vary slightly in the way that they do these calculations, which may result in noticeable differences in your HRV score between Core and other apps.
The way the Core App calculates your HRV Score is as follows:
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Where rMSSD is the root mean square of successive differences in RR-Intervals - a metric of HRV that is strongly backed by research and is considered the most relevant and accurate measure of Autonomic Nervous System activity over the short term. We transform this measure to an HRV Score using the equation above to fit in a 0-100 scale that’s more interpretable, a common method used on other apps.
This is another reason you should worry less about the absolute value of your score, and pay more attention to relative change over time. The number itself is less important than how your HRV is trending, or whether your score after a meditation is significantly higher or lower than your usual.