Apple website (https://support.apple.com/en-gb/HT204666) states this: "HRV measurements aren't available in China, Malaysia, South Africa, and Turkey." I've got an Apple Watch S2 from China on watchOS 4 and indeed I cannot get it to measure the HRV. With that said, I'm neither Chinese nor am I based in China (or any of the above countries). I'm in the UK and the watch is set up with the UK locality so I'm puzzled as to why I'm not getting HRV measurements. Are Chinese watches physically different, i.e., is there a piece of hardware missing from them?