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Comment by nradov | Hacker News Reader

Who is "you"? I have the training and sometimes go significantly deeper. I use a competing Garmin smartwatch, works great. Do you understand why?

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How deep are you going? What gas mixtures are you using? Which Garmin are you using? If you're using a Mk3i or a G2 (or related) you are using a diving computer in a smart watch form factor. It is custom built for this... unlike the Apple Watch Ultra.

I'm still using the older Garmin Descent Mk2 model, which is basically equivalent to the Mk3 for diving features. (I might upgrade to the Mk4 when it launches later this year.) It sure is handy to have a single smartwatch that can do everything.

We use a variety standard breathing gas mixes for the depth range based on limits imposed by density, narcosis, decompression time, and oxygen exposure.

You go significantly deeper? You're aware that shortly past 50mt the partial pressure of oxygen causes neurotoxicity, leading to convulsions and death? Anything happening past those depths involves extremely expensive hardware, custom trimix breathing gases and most importantly a hell of a good reason to even bother doing it - that is NOT the environment for an Apple Watch.

Yes, I go significantly deeper. You seem to be a little confused about how oxygen toxicity works but rest assured that we're aware of it and use appropriate breathing gasses for the depth.

I understand that an Apple Watch Ultra can't be used for those dives, and that's fine — they don't need to support every possible niche use case. But competing smartwatches from Garmin and Suunto do handle deeper dives and the associated gas mixes. There's nothing stopping Apple from doing the same if they want to.

> You seem to be a little confused about how oxygen toxicity works

Thanks for the condescending tone. Am I?

At 1.4 bar of O2 partial pressure (therefore, with a 21% breathing gas mixture, at around 66m depth), oxygen toxicity causes convulsions and unconsciousness. If someone doesn't grab you and take you up, this likely results in death.

Btw I had to google the precise values and depths to be accurate, but I'm not talking out my ass. I'm a certified CMAS and AOW diver with 80ish logged dives. Hardly a veteran but this was in my certification course and it's a very real thing - enlighten my confused state with your better knowledge please.

You're talking out your ass and unclear on the basics. Obviously we're using standard gas mixes based on the depth profile, not compressed air. For the working portion of the dive we generally limit PPO2 to 1.2 atm but will go as high as 1.6 for portions of the deco. If you'd like to understand diving physiology instead of just repeating what you Googled then Bennett and Elliott is a good place to start.

https://www.us.elsevierhealth.com/bennett-and-elliotts-physi...

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