Sleep is something I think (and write) about a lot. And after years of interviewing doctors who specialize in the essential human function, it’s become clear to me that quality is more important than quantity.

That is, spending eight hours in bed at night doesn’t necessarily guarantee that you’ll wake up refreshed the next morning. Sleep quality is more dependent on how much time you spend in the two last stages of sleep: REM and deep sleep, or slow-wave sleep. Those later stages are where the body recovers from the day and the brain flushes out waste and consolidates memories.

Unless you’re sleeping hooked up to an ECG, it’s impossible to know how long you actually spend in these later stages every night. But personalized sleep trackers, while not perfect, can give you a pretty good read on what’s happening under the hood when you’re snoozing.

Curious to learn more about my own sleep quality and what influences it, I connected with the team at Oura, who were kind enough to give me a tracker to try. What’s unique about Oura is its ring design. Beyond being more comfortable to wear to bed than a watch, Oura CEO Harpreet Rai explained to me that the ring had a functional component too: Our fingers tend to have a stronger pulse signal than the front of our wrists, which Oura says allows them to take more accurate readings throughout the night. It uses this to approximate the amount of time you spend in the various sleep stages.

The ring also provides data on other factors that could be relevant to sleep quality, like average resting heart rate and body temperature (interestingly enough, some clinical studies have tested the ring for early COVID detection.)

Clearly, “good sleep” doesn’t rely on just one thing. “Sleep is a complicated metric to measure,” board-certified sleep specialist Michael Breus, PhD, said of sleep trackers during a recent event with mattress company Hästens. For this reason, he recommends using trackers to measure any sleep trends that occur over time and not getting too hung up on the numbers that come in nightly. “It’s not about the absolute data; it’s about the relative data,” he added.

With this panned-out perspective in mind, I started tracking my sleep in early January and have looked out for insights on what helps and harms sleep quality along the way. Here’s what the experience has taught me about the factors that get in the way of deep, restorative sleep, at least in my bedroom: