I was using a few wearables to measure my HRV - and it seems that the data across different wearables are inconsistent.
Here’s the summary on the comparison between Oura and Polar (i was using an Oura ring 3, vs a Polar Unite) (and yes those two are different price points)
Polar HRV is consistently higher than Oura and Polar’s HRV readings are more volatile than Oura’s in general.
Both wearables record spikes in HRV data, up to a 30ms jump in HRV in Polar’s case which is a huge change.
Not much consistency between Polar and Oura’s measurements to compare HRV trends, unlike for heart rate.
The differences in HRV between Polar and Oura could be because Oura takes readings from your finger while Polar uses your wrist, especially for a metric as sensitive as HRV.
I wrote a full guide with the data and graphs here