Depth Reading Discrepancy

Paul Brookes

Hi all

A rambly text, then I’ll get to my question…

I currently dive an inspiration with a 4th cell connected to a VR3 (CCR Nitrox)
I then have a Suunto Vytek in guage mode as back up depth gauge and timer.

In the 100 or so Rebreather dives I have done to date, the 2 computers have been pretty consistent in their depth readings, never more than 20cm between them. However, I was diving yesterday on the Betsy Anna out of Swanage and got a pretty significant variance between the two.

During the dive, I didn’t notice an issue, with both reading around the 24m mark (although I admit I did not have them side by side). At around 15m, I brought the VR3 and master handset up next to the Vytek so I could see the handset and both computers whilst reeling up and noticed that they were over a metre apart in their readings. The VR3 showed the deeper reading. I compared both with my (OC) buddy’s Suunto Stinger and his was the same as my Vytek. At the 5m safety stop, the VR3 was still reading 6.3m.
Unfortunately, in the last few metres, my buddy got too buoyant and I had to assist him to the surface so I did not see what happened when the VR3 got to the surface. I am therefore assuming that the VR3 was at fault.

Now, the wreck is only in 25 metres, and with spring tides this weekend, there was never any planned decompression so there were no stops carried out at the wrong depth. Also, I haven’t dived since, so I do not know if this was a one off. However, this has concerned me somewhat as it could have been more serious.

I know that depth readings can vary at depth, but I have not heard of them being so far out at shallow stop depths. Has anyone had a similar experience? What did you do about it? Should I monitor things over a few more no stop dives before sending the VR3 off for inspection?

Thanks, Paul

gallathan

Me and my buddies dive inspirations, and use several makes of suunto D3, mosquito/ vytec / vyper as bottom / depth timers, and the vision, vr3 and hs explorer as primary computers. We also have and do use uwatec bottom timers too. In our experience, up to a metre discrepancy in depth is NORMAL.
If find the Explorer / suuntos track each other rather closely, the uwatec and the VR3 tend to read up to a metre deeper. Just read a post on rebreather world about vr3 vs explorer that shows depth readings on VR3 are perticularily accurate... I do generally find that the readings get closer together when going shallower. I noticed that as I wear them on different arms, that if i hold my arms at different depth I get different readings.. Suspect once the batteries get low / in colder water (which is harde on batteries) then occasionally I see more discrepacy - maybe happended once every 200 dives. I HAVE had a depth sensor fail on boh an explorer and the suunto - in both cases they started reading deeper - a LOT deeper, that caused me a few anxious moments. I have also have several uwatec timers that when surface were still convinced they were at 3 to 6m. All these were symptoms of a flooded / trashed computer SIGH. I'm not saying its the best answer, but our solution is to assume the shallowest depth is correct and stop there. Why? Because we don't want to violate the deo ceiling, so if we hang a little below it and off gas a little slower, its better than exceeding it. Most computers will account for slower off gassing, so we clear ALL the stops on ALL the computers before exiting water. Hope this helps

decoweenie

IMHO it is not normal for that much off in your case.

Depth readings are off between some computers since some are calibrated in freshwater, some in saltwater and some has automatic routine to adjust (I guess measuring the resistance in water ?), but I haven't seen 1.5m off at 5m depth.

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