I had planned to do an extensive writeup on the
Oura Ring, but was waiting until I had at least two weeks of use under my belt. I will get there, but in the interim,
Ben Greenfield did a thorough job of providing an overview of the Oura's capabilities and the nitty gritty of sleep stages. It is a long read but contains a lot of great information.
Everything You Need To Know About Sleep Cycles (And Four Ways To Hack Your Sleep Cycles)
Enjoy!
Chuck