Ever seen a computer malfunction in this way?

[Fastmarc]

So it's not odd that 2 computers on the same arm would vary this much? The 6 mins on the 1st Is not terrible, but 43mins on the 2nd?

 

[KenGordon]

So it's not odd that 2 computers on the same arm would vary this much? The 6 mins on the 1st Is not terrible, but 43mins on the 2nd?

No. As you get shallower your NDL times will exaggerate the differences in the limits the models set on over saturation.

 

[RonR]

Ken is exactly right. Computers have to treat NDL’s as if they are a binary switch that gets thrown, rather than what they actually are- which is a fuzzy gray area. Particularly at shallow depths even relatively minor differences between algorithms can result in large differences in displayed NDL times.

 

[scubadada]

@Fastmarc

If you think your Mares became more conservative than it used to be, at the same setting, I would suspect the pressure sensor is malfunctioning. Use the planner to generate a list of NDLs, and compare with another, comparable Mares computer. Of course this will only be 1st, clean dive. Though this doesn't reflect behavior on repetitive dives, if 1st dive is good, it is less likely to be the sensor. I had one Oceanic PP2 that was intermittent until it went out permanently

 

[Fastmarc]

@Fastmarc

If you think your Mares became more conservative than it used to be, at the same setting, I would suspect the pressure sensor is malfunctioning. Use the planner to generate a list of NDLs, and compare with another, comparable Mares computer. Of course this will only be 1st, clean dive. Though this doesn't reflect behavior on repetitive dives, if 1st dive is good, it is less likely to be the sensor. I had one Oceanic PP2 that was intermittent until it went out permanently

Prior to diving with the perdix, I did a planning comparison with the mares, with perdix at GF45/95. They were very close, either dead on or within 1 min of each other at various depths, for the 1st dive. The mistake I made was not doing that during the SI. I thought of it on the boat, but it slipped me by the time we got back to shore to change tanks.
I have about 150 dives on it, so I know it well. I rarely come across another diver with a mares, mostly suunto, but even so I have always been able to dive normally, never pushing my NDLs and I've never noticed having to sacrifice my BT compared to others. Well, not until recently. I'm pretty sure something has gone wrong. Just curious what it could be and if this was common. I have no intention to dive it again and since it was well used, no intention sell. I did flirt with the idea of it being a backup if I went on a dive trip, but will pick up the Deep 6 for that now.

I do have another Mares that I could compare it to. I guess I could just stick them both in my pocket and look at them after the dives. I didn't want to dive the other one though as I wanted to possibly sell it. It's the original Nemo titanium in pretty good condition. I haven't dived it for years, but always had it ready to dive, keeping the battery fresh which was just changed. I stopped diving it because being in Jamaica and a year round diver, it was a pain to have to send it to the US to get the battery changed.
If I do it, I'll report back.

 

[tursiops]

if 1st dive is good, it is less likely to be the sensor

I'm not following your logic here. Isn't the plan mode just software? How is that related to the pressure sensor?

 

[Belzelbub]

I saw that you used two different e-logs for the two computers. Try downloading the days dives from the Nemo using Subsurface. I noticed a little while ago that the same dive using the same computer was showing different NDLs at the same point in Diverlog and Subsurface. I poked around a bit and found that Subsurface was calculating the NDL using Buhlmann w/GFs. Set the GF to match what you were running on the Shearwater, and look at the profiles and NDLs again. This should eliminate the algorithm as a variable since Subsurface just takes the depth and time info and uses the Buhlmann algorithm to calculate the NDLs. If it is pretty close, then the difference is the algorithm. If still off significantly, then you may have an issue with one of your computers.

I suspect it’s the algorithm since the profiles looked pretty similar.

Here's an example. Same dive, same computer, pointer positioned at 16:25 into the dive. This was the only dive of the day. First picture is from Diverlog. Computer was set to DSAT algorithm. Note NDL is listed as 17 minutes.

Second picture is from Subsurface. You can't see the pointer as in the Diverlog version, but my mouse was positioned right at the point just before starting the ascent. This was with Buhlmann 40/85, but you can change that to whatever value you want. Set that to what you are running on your Shearwater.

As you can see, despite these being taken from the exact same dive computer on the same dive, the NDLs were different. 17 minutes for DSAT, and 7 minutes for Buhlmann 40/85

 

[scubadada]

I'm not following your logic here. Isn't the plan mode just software? How is that related to the pressure sensor?

I had 3 separate Oceanic Pro Plus 2s that, when quite old, started displaying in correct NDLs, less than expected. They were displaying the NDL for the next higher altitude, 3000 feet. This is how Oceanic does conservative factors, next highest altitude. I contacted Oceanic or, later, Huish, and was told it was the pressure sensor. I had all three replaced with new or refurbished units and they are still working perfectly today. None of them ever gave an Incorrect depth during a dive, only incorrect NDL. The cause given by Oceanic could be incorrect and it may have been another cause, just what I was told independently on 3 occassions. It appeared that they were quite used to dealing with this problem.

 

[Centrals]

Two completely different approaches on the last 5 mins(safety stop) by Fastmarc and Belzelbub. A more or less constant level at 6m for "Bel" and then a further short stop at 3m before surfacing. This is what I normally do.

 

[Jay]

I saw that you used two different e-logs for the two computers. Try downloading the days dives from the Nemo using Subsurface. I noticed a little while ago that the same dive using the same computer was showing different NDLs at the same point in Diverlog and Subsurface. I poked around a bit and found that Subsurface was calculating the NDL using Buhlmann w/GFs. Set the GF to match what you were running on the Shearwater, and look at the profiles and NDLs again. This should eliminate the algorithm as a variable since Subsurface just takes the depth and time info and uses the Buhlmann algorithm to calculate the NDLs. If it is pretty close, then the difference is the algorithm. If still off significantly, then you may have an issue with one of your computers.

There could also be these issues as per the quote below from SubS

Here is what I came up with when analysing your dive 105 in Subsurface: First of all, the NDL/TTS calculation is somewhat resource expensive as for each value a full decompression plan has to be calculated. Therefore, Subsurface does not really compute this value for each waypoint of the dive profile but only once every 30s of divetime. Plus it makes some simplifying assumptions like the end of NDL being the time a ceiling appears (which is shorter than the time we could stay at the momentary depth without any stops on the way up as the ceiling might already clear on the way to the first stop).
If you want more accurate data, you should select Log->Edit dive in planner from the menu. There you can remove all profile points after the 15min mark by Ctrl-clicking on the dustbin next to the corresponding segment in the table (Ctrl means delete all further waypoints not just one) and then use the recreational planning mode which is kind of a pimped NDL calculation.
When I first did that I got a maximal stay at that depth of 23min, much closer to what there Shearwater value is. But then I realised that around the interesting time, there is quite some depth variation in the profile: In about 40s, you ascent from 26m to 22m. But of course, for a given tissue saturation, the NDL depends on the current depth. And those 23min were for a depth close to 22m. So I adjusted the depth to 26m and there we are: That makes all of the difference as at that depth, tissue loading is so much faster that you can stay only another 13min without incurring a ceiling. So all the difference is in the depth you use to calculate the NDL. So Subsurface has picked a profile point (remember it does that every 30s) that was significantly deeper than the profile point that Shearwater used to compute the NDL.
Does this make sense?

(above quote was from this thread: SWCloud and Subsurface differences )