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OSTC Plus wanting more deco than i think it should
My girlfriend has recently got an OSTC Plus (in sport mode) and it seems pretty nice. I'm thinking of changing my old OSTC mk2 over to the newer model so I took it for a couple of dives at Chepstow yesterday to try it out but I was surprised at the differences in deco between the two of them. The OSTC Plus seems to accrue deco faster. Both computers set to OC ZH-L16-GF 30/85. My older OSTC mk2 seems to agree with Subsurface (my dive logging tool) reasonably well but this newer one seems a bit off, quite a bit off in some circumstances.
It also doesn't seem to want stops deeper than 6m (at least in the logged dive I did). The simulator seems to behave correctly when I try it on a made up dive but when I download the logs to look at the new computer is asking for quite a long stop at 6 where as both the old computer and Subsurface switch over to wanting a deeper stop.
Examples of strangeness are that it jumped from wanting 12min at 6m straight to 28min at 6m (I was at about 19m when this happened) and then on the next dive it jumped from wanting 6min at 6m straight to 15min at 6m (I was at 18m at the time) that seems a bit excessive. The older computer at the same point in the dive was asking for 1min at 9m followed by something like 6min at 6m for the first dive and on the second dive it didn't want any deco at all.
Anyone seen similar? Doesn't fill me with confidence for this new computer.
Running 10.53 firmware.
I've maybe found something.
In the deco conservatism settings the new computer was set at 0 (which would make you think nothing was added) but there is actually a GF setting. I have set the computer to this and just starting the simulator again to see if that lines up better.
...and sell your MkII on here
How much are you offering?
It's been a great computer for me. It does exactly what I want and if I did want to tweak something (final stop depth or future TTS or something like that) then there is a setting to do that.
That setting I found does seem to help, the times are still slightly different when running the simulator with the Plus being more conservative but only by a couple of minutes or so. I was thinking of lowering my GF High a little bit anyway so this is probably fine with me. I will likely take it on at least one more real dive before I make a decision.
Christ, just noticed that in all this fiddling I ended up resetting my old computer to straight ZH-L16 rather than ZH-L16-GF. Ok, off to run the simulator again then.
Last edited by jb2cool; 12-08-2019 at 11:41 AM.
I've got the 2N - love it... wouldnt swap it for any other make...not sure what the MkII's are going for
My computer always gives too much deco - I just ignore it 🤣
I can't help you with he details, but I *can* tell you that OSTCs support two conservatism modes: tried and true generic gradient factors (which mess with the a and b coefficients) and HW-specific "conservatism factors" (which mess with tissue time constants).
Originally Posted by jb2cool
Update for completeness. Conservatism set to GF rather than 0 worked great and computers are now agreeing perfectly.
There have been slight changes to the deco calculations across the firmware versions. Itís explained in quite some detail on the HW forum what was changed and why. Maybe thatís the reason?
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