u/userX97ee2ska11qa

This really surprises me.

After a year of cycling against after nearly 25 years, and racking up about 5,000 miles, I think I agree with this video. I played with my fit myself adjusting as I went until I found what was right. In that year I had a few LBS tell me how to adjust my bike just in casual conversation.

I’m a heart patient, and after 26.6 ECG readings seem to fail and restart in the middle of the reading or show inconclusive results. I’ve confirmed with my doctor that there isn’t a heart issue, but I noticed it on my watch. Anyone else?

My Best Buy finally has demo models of the Amazfit watches, so I heard, and I rushed down to look at them. Finally excited to maybe get a T-Rex and turns off their dummy plastic models and basically stapled to the display counter. You can’t even lift them up or see them or anything. I really don’t know how Amazfit expects to sell any watches this way. I’m just going to give up on them I think. Such a shame.

I don't mean cleaning it for maintenance, I mean cleaning it to make it look nice. 

I used Maps to create a custom route to test and then tried it on a trail in the woods. This is a marked trail with pretty much no risk of getting lost on. Signs are at every fork. My expectation was that it would be able to give guidance via notifications when I should make a turn. It did not. No focus mode was enabled, and all settings were so that it should have worked that way. Are my expectations simply wrong? Have you tried it? How did it work for you?

Anyone know if 7 Mile Rd. in Gouldsboro is open to motor vehicles right now?

I used the Maps app on my iPhone to create a custom route for testing on my Apple Watch while hiking on a marked trail in the woods. The trail is well-marked with signs at every fork, making it unlikely to get lost. I expected the watch to provide turn-by-turn notifications, but it did not. No focus mode was activated, and all settings were configured correctly for it to function as expected. Are my expectations incorrect? Have you tried this feature? How did it perform for you?

I used the Maps app on my iPhone to create a custom route for testing on my Apple Watch while hiking on a marked trail in the woods. The trail is well-marked with signs at every fork, making it unlikely to get lost. I expected the watch to provide turn-by-turn notifications, but it did not. No focus mode was activated, and all settings were configured correctly for it to function as expected. Are my expectations incorrect? Have you tried this feature? How did it perform for you?

TLDR: Long post, but short version: your watch isn't measuring sleep stage, it's guessing based on movement and heart rate. It's decent at telling asleep from awake, more of a coin flip on Deep vs Core vs REM. All four major brands land in roughly the same accuracy range, so no one has a real edge here. Good for spotting trends over time, not a substitute for an actual sleep study.

Apple Watch doesn't read your brain. It never has. The only way to actually know what stage of sleep someone's in is a lab sleep study, polysomnography, which reads brain waves, eye movement, and muscle tone directly. A watch has none of that. It's guessing based on secondhand evidence: how still your wrist is and what your heart's doing. That's not an Apple problem specifically. Every wrist tracker on the market works this way. Keep that gap in mind for everything below.

Here's what it's actually measuring. The accelerometer tracks wrist stillness. Almost no movement for a stretch is the strongest signal you're asleep. The optical heart rate sensor tracks pulse, and heart rate drops and smooths out as you go deeper into sleep. HRV, the beat to beat timing variation, shifts depending on sleep stage and is one of the main things the algorithm uses to sort stages. Wrist temperature drifts in a predictable overnight pattern and helps confirm timing. Blood oxygen and breathing rate mostly feed other features like apnea notifications, but breathing stability adds supporting evidence too.

Every 30 seconds the model takes all of that and buckets the window into Awake, REM, Core, or Deep. Core is Apple's term for regular light sleep, it's most of the night for most people. Deep is slow wave sleep, the physically restorative stage, hardest to get and most valuable. REM is the dreaming stage, body mostly paralyzed, brain and heart rate active.

Sleep Score itself came with watchOS 26 and the Series 11, September 2025. Single number, 0 to 100, with a label: Very Low, Low, OK, High, Very High. Three components. Duration is 50 points, how much you slept against your sleep goal. Bedtime consistency is 30 points, how much your bedtime varies over roughly the last two weeks. Interruptions is 20 points, how often and how long you woke up overnight.

Worth noting: the score doesn't grade Deep or REM amounts directly. It's a behavior score, did you sleep enough, on a consistent schedule, without much waking. Stage breakdown still shows separately in Health, it's just not part of the 0 to 100 number.

On accuracy, split it into two questions because the answers aren't the same. Telling sleep from awake is the easy part and the watch is good at it, roughly 90 to 98% correct in validation testing. Where it slips is quiet wakefulness, reading in bed, scrolling your phone, resting still, that can get logged as light sleep since stillness is the main signal it's reading.

Telling the four stages apart is harder, and every wrist device gets fuzzier here, not just Apple's. Researchers use Cohen's kappa to score agreement between two "scorers," correcting for chance. Below 0.40 is weak, 0.40 to 0.60 is moderate, above 0.60 is substantial. Two human PSG technicians scoring the same night against each other land around 0.75 to 0.80, so even trained experts don't fully agree. Apple's four stage agreement against lab PSG runs about 0.5 to 0.6 in published work, moderate, sometimes substantial. Most common miss is Deep logged as Core, watch tends to undercount true deep sleep. REM detection is a bit better but still imperfect. Same pattern shows up industry wide because it's a structural limit of using movement and heart signals as a stand in for brain activity, not a flaw specific to Apple's code.

On Garmin, Fitbit/Pixel, Samsung: all working off the same basic inputs, motion plus heart rate sensor on the wrist, so raw accuracy lands in a similar range across all of them. Real differences are in emphasis and extra features, not stage detection accuracy.

Garmin runs on a Firstbeat derived engine, adds HRV and blood oxygen on some models, ties sleep scoring into recovery and Body Battery. Built with training load in mind. Stage accuracy is moderate, a bit more variable device to device than Apple.

Fitbit and Pixel Watch use motion, HRV, skin temperature, blood oxygen on some models. Score weighs duration, time in Deep/REM, and restlessness. Fitbit has the longest published validation track record of any consumer wearable, which counts for something even though the accuracy numbers land in the same moderate range as everyone else.

Samsung's BioActive sensor adds ECG plus skin temperature. Scoring focuses on sleep cycles, movement, physical/mental recovery. Less public stage validation data than Apple or Fitbit, but it does have FDA cleared apnea detection.

None of these four reliably beats the others on core stage accuracy. Real differences are in extra features and how much validation data each company's actually published, not some hidden accuracy edge.

The gap between watches and real sleep studies isn't closing anytime soon, and it's not a software problem. A lab study reads electrical activity straight off the scalp. A watch infers stage indirectly, on the logic that stillness plus a slow steady heart rate usually means deep sleep. Usually isn't always. Quiet wakefulness looks like light sleep to a motion sensor, which inflates reported total sleep time. And signal quality varies night to night, a loose band, a cold room, a restless arm can weaken the heart rate read for stretches of the night, forcing the watch back onto motion data alone, which is the least precise input for telling stages apart.

These devices are genuinely useful for trends over weeks and months, duration trending up or down, bedtime drifting, interruptions increasing. Any single night's exact stage split should be treated as an estimate, not a measurement.

A few things throw the numbers off for specific people. These algorithms are trained mostly on typical healthy adults. A naturally low resting heart rate, like in endurance athletes, can get misread since the model expects a certain magnitude of drop to signal deep sleep, and someone already bradycardic at baseline doesn't drop the same way. Heart rate affecting meds, beta blockers for example, blunt the rise and fall the algorithm relies on for stage transitions. Irregular rhythms disrupt the beat to beat pattern used for HRV, sometimes forcing the watch onto motion data alone. Sleep position constraints, back sleeping only for instance, can loosen wrist contact and add noise to the heart rate signal. None of that makes the data useless, it just means trends over time matter more than any single night's exact numbers for anyone in one of these categories.

Sleep Score is a simple, transparent formula, duration, consistency, interruptions, sitting on top of a much less transparent machine learning stage classifier underneath. That classifier is decent, moderate to substantial accuracy against lab studies, and it shares the same basic limits as every other wrist tracker out there. Good for trend tracking and flagging things worth bringing up with a sleep specialist. Not a substitute for an actual sleep study.

As a bike mechanic, how would you compare Advent versus Cues?

I’m new to having a derailleur with a clutch, and I was told that the clutch can affect shifting performance. When do you personally enable or disable the clutch?