New way to track REMnon an old device

As you know, I’ve been using both an iPhone recorder app to record elements of my dreaming, as well as another iPhone app that records whether I’m snoring etc. I have an Apple Watch Series 4, which is several years old but now because of a new software update that came yesterday (Watch OS9) it now tracks sleep cycles. And today I compared what it recorded with the various time stamped recordings that I have of my dreaming and snoring last night and there’s a really good match. I’m very impressed. Here is a YouTube channel that I used to follow that has come to a somewhat similar conclusion, about the accuracy of what it tracks .