Some Polar equipment does HRV and orthostatic HR. I've been using a V800 GPS watch for several years. Not made anymore, but still supported, on ebay, and never had a problem with one. I very much like the orthostatic HR feature which also includes HRV. Battery life isn't long enough to record long bike rides using GPS, my only complaint. 4 hours is probably the limit. I use my Garmin Edge for that.
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