Geo 2.0 and VT4 algorithms

My partner and I are in Bonaire this week, diving a ton. He has a Geo 2.0 and I have a VT4. Both are set to the DSAT algorithm with conservative factor set to off. Both of us have been diving the same profiles (average depth has varied a little bit but no more than a couple of feet and not consistently one direction or the other) with EAN32.

At the beginning of a dive day, both computers have the same TLBG bars (none) and in planning mode produce the same results for the same depths. However, after a day of diving, the Geo 2.0 ends up with much shorter desaturation time remaining, fewer TLBG bars and longer NDLs than the VT4. Last night after our fourth dive of the day, the VT4 had 4 bars, while the Geo 2.0 only 1 and the NDLs in plan mode were almost half as long on the VT4.

I was under the impression that these computers run the same algorithm, but maybe something else is going on. Has the algorithm been tweaked in newer computers or is there some other setting I'm possibly overlooking?

On my VT4, there's some kind of safety factor setting that's only accessible from the pc. It ranges from 1-12, and i believe it's related to the TBLG calculation. You might start there?

They should be the same. How about that 50% default FO2 setting? I honestly don't remember what it does but I seem to recall on my Geo, the factory setting was ON

I also seem to think someone very recently posted about their VT4 computer basically not counting "off-gassing" during surface intervals: http://www.scubaboard.com/forums/oc...ad-not-receeding-deco-1min-into-3rd-dive.html

I had a problem with my VEO 200 when using the 50% Default "OFF" which I discovered while diving a VEO200 and a Data Plus right next to each other.. The VEO 200 indicated it was 32% O2 but appeared to be defaulting back to 79% N2 for NDL calculations. I switch to default "OFF" and the discrep[ancy disappeared. If it is running default "ON' try switching it to default "OFF" and resetting your mix each dive. Please let me know if this has any effect.

CT Sean:

They should be the same. How about that 50% default FO2 setting? I honestly don't remember what it does but I seem to recall on my Geo, the factory setting was ON

I also seem to think someone very recently posted about their VT4 computer basically not counting "off-gassing" during surface intervals: http://www.scubaboard.com/forums/oc...ad-not-receeding-deco-1min-into-3rd-dive.html

Click to expand...

This setting is only supposed to make the computer reset to 50% nitrox before each dive, forcing you to manually input your O2 content.

That being said, it looks like some have found bugs with this setting, so who knows.

Sent from my phone.

It looks like the same problem mentioned in the linked thread. After two more relatively shallow dives today (1 hour to 18m followed by a 45 minute SI then 1 hour to 13m), the VT4 went into 260 minutes of deco at 3m immediately upon descent. That doesn't make sense with any sane algorithm. Looks like I'll need to get the unit serviced by Oceanic. My backup computer should be good to go for tomorrow though but no air integration. Bummer.

If you could post your dive profile from the computer download it would really help identify which one has the problem.

I have a VT3 and a Geo2 I've been diving together for 14 months. They always show the same NDL within 1 minute. I've dived as many as 25 dives in a week. They sometimes vary a small amount in desaturation time, but by no more than 10 minutes or so. The Geo2 always goes into deco just before the VT3. I dive them both in DSAT without conservative factor. I like it that the Geo2 continues to show my NDL when my VT3 is limited by air time. For me, these are the ideal primary and backup computers. I do have a SPG in case AI ever fails, not once in 2 1/2 years and 240 dives.

You may want to see if you have latest firmware version. I had problems with my VT4.1 as detailed in the linked thread.

I realized I never came back to tell the rest of the story.

After I got back from Bonaire I called Oceanic and they told me to send it in. I don't recall how long it was gone for but I want to say it was a couple weeks. I didn't get any notice that it was done or being sent back. It just arrived one day on my doorstep without much explanation of what was done to fix it. It was apparent to me that it was either a new or refurbed unit because the light scratches on the screen were all gone.

I've been diving it for the last 6 months seemingly problem-free. The desaturation times and TLBG still differed from the Geo 2.0 but not by a whole lot like before.

Everything seemed to be fine until I went on another multiday dive trip a couple weeks ago, this time to God's Pocket in British Columbia. After the first dive on the third day, I came up with 3 bars on the TLBG after a 38 minute dive on Browning Wall to a max depth of 78ft, average depth of 53ft with a very gradual ascent on EAN31. The 3 bars remained after more than 3 hours into the surface interval. I could see that the same problem as before was back. Instead of waiting for the computer to go into deco on the next dive, I popped it into gauge mode and used my backup for NDL time for the remaining two dives of the trip/day.

It's now back at Oceanic a second time in 6 months for what appears to be the same or a very similar problem. Pretty disappointing.