Apple Watch Ultra Ascent Rate Questions

[ccphares]

I have been using the Apple Watch Ultra as my dive computer for two trips - Cabo and the Florida Keys - and have 8 dives logged. During my trip to the Keys, I noticed I was seeing very high max ascent rates on my dive logs. I was pretty surprised by this so I wanted to dig into the data and see when this was occurring.

First, here is a screen shot of one of the logs in question:

You can see that it reports a max ascent rate of 111ft/min (!!!) but the color coding on the chart shows that I was only in the 30ft/min range a few times during my dive. I can understand than maybe some short durations could have exceeded that, and just are too short to visualize on the graph. So, I wanted to dig in a little deeper...

I got the AWU2UDDF app, and converted my logs to XML files. I then wrote a short Python script to get the data into a csv file. The file has a data point every 2.649 seconds. Here's a plot of my dive data with the ascent rate and the depth vs. time. As you can see, I do get close to the 60 ft/sec band, but I don't see anything at 111ft/sec.

So, here are my questions:

1. Does the watch have the ability to record and process data more frequently than what is being stored in the health app?
2. If so, and the 111 ft/sec rate is real, but occurred for a duration less than 2.65 seconds, should I be concerned?
3. I am guessing that some of the fast rates are due to the watch being on my wrist, and I was using a mooring line for the ascents, and so my hand could move more quickly up the line than the rest of my body. Is that a concern?


Looking forward to some thoughts on this.

 

[inquis]

If so, and the 111 ft/sec rate is real, but occurred for a duration less than 2.65 seconds, should I be concerned?

You waved your arm. No big deal.

 

[OrcasC205]

As the developer, I'm glad you found the AWU2UDDF app useful. Because the API to get data from the depth sensor for the dive computer app requires an entitlement from Apple that is not publicly available (yet), I don't know if they are seeing a faster sampling rate than the data being stored in HealthKit, but I wouldn't worry about it from a physiological perspective -- the pressure changes would need to be more extreme and/or more prolonged before there should be any physiological decompression impact.

 

[Lostdiver71]

I have had the same problem on every dive logged by the Apple Watch so far despite my other dive computer not showing an ascent rate faster than 60 feet per minute! It seems to be a glitch with the watch.

 

[Rick Brant]

I think inquis has it right. I have gotten an ascent warning when moving my arm rapidly. I think you have to time it just so to get that though. It would be good if they could bake the accelerometer into their ascent reading to see if the whole person is moving or just the arm.

 

[jborg]

Or just calculate ascent rate as the average over several ft/m of average ascent, ignoring however fast the watch moved two inches… this just seems like a sloppy/unpolished implementation.

 

[ccphares]

Thanks for all the replies. Are there any DAN or PADI articles that talk about what duration of fast ascent rate is significant for nitrogen bubble formation? Also, if you raise your hand quickly, can you get nitrogen bubbles in your hand? That may seem like a silly question, but I have always assumed that the ascent rate of your heart/lungs/brain was the critical part. Maybe I am wrong.

 

[OrcasC205]

I am not aware of any articles that address it, but from a logical perspective even if you move your hand from straight down to reaching straight up, you're talking about 4-5 feet of depth change at most -- that's not a significant change of pressure even at shallow depths. Even if you are just under the surface (like at 3 feet depth), is is like 1/6 of an atmosphere pressure difference (at most).

 

[ccphares]

That's a great point. I had not thought of it like that.

Also, nice job on the app. An option to export to CSV or tab text would be a nice addition.

 

[OrcasC205]

That's a great point. I had not thought of it like that.

As I reread that I realized I confused things a bit -- a five foot change in depth is always about 1/6 atmosphere whether shallow or deep. It is the percentage change that gets greater the more shallow you are.

Also, nice job on the app. An option to export to CSV or tab text would be a nice addition.

Thanks. I'll add those to the backlog and see if I can figure out a way to have that option. The UDDF was easy because it is a documented standard -- I'm not sure something similar exists for CSV or tab separated data (not that it would matter if it's just being imported into a spreadsheet to be manipulated.)