Computer issue or DM issue?

[lmcgill97]

Hi! The issue I'm having is making me quite nervous, so I hope you can help. I have two Vyper computers (both purchased used). After a three dive day in July, I downloaded my dives and saw that the download said I went into deco. My computer didn't indicate that in real time during the dive. I deleted and redownloaded the dive, and the NDL times through the profile changed for the same dive and now no deco was indicated. Being worried about this, I wore a computer on each wrist on a recent three dive day and compared them frequently on the third dive. They didn't agree with each other (e.g. one would have a 5 min NDL when the other had 12 min), but neither one showed an ascent time or a ceiling at any point (I was checking them every minute or so). When I downloaded them, both show ascent times and ceilings for a large part of the dive! I have downloaded both computers into DM3 and DM5, and the two versions of DM disagree with each other for the same dive. I'm getting to the point where I don't trust either computer and am tempted to replace them with another brand. Is there any way for me to know what to trust? Thanks! -Lisa
P.S. I just deleted and redownloaded the recent third dive in DM3, and now one computer shows what I saw during the dive (no deco), whereas on the previous download it showed ascent time and a 10 minute ceiling. The other computer still says I was in deco for 20 minutes... I wear both computers on all dives

 

[BigJeff]

I have seen this with my computers (Mosquito & Cobra) when using DM3. The downloaded dives show deco in DM3, but computers real time on the dive do not.
This only happened when my NDL went below 10 mins after multiple dives.

It may be due to the difference in sample rates as the computer uses every second to calculate in realtime but DM can only use the data downloaded to calculate, which is depth every 10 or 20 seconds.

I would trust the NDL calculated realtime underwater, the NDL calculated by DM3 is an estimate based on less data.

 

[muzikbiz22]

MacDive

 

[Freewillow]

are you sure that your 2 Computors have the same "safety" settings?

 

[lmcgill97]

are you sure that your 2 Computors have the same "safety" settings?

Yep, both are P0/A0. I do have them set to different sample rates for download, but I'm not sure if that matters in real time on the dive?

---------- Post added August 29th, 2015 at 08:55 PM ----------

I have seen this with my computers (Mosquito & Cobra) when using DM3. The downloaded dives show deco in DM3, but computers real time on the dive do not.
This only happened when my NDL went below 10 mins after multiple dives.

It may be due to the difference in sample rates as the computer uses every second to calculate in realtime but DM can only use the data downloaded to calculate, which is depth every 10 or 20 seconds.

I would trust the NDL calculated realtime underwater, the NDL calculated by DM3 is an estimate based on less data.

That sounds just the same as my issue! I didn't realize DM was calculating NDL from the profile info, rather than downloading it from history on the computer. Thanks for the info , that makes more sense.

 

[Chicken SCUBA]

Does the viper have the option to chose between RGBM50 and RGBM100 like many of the older suunto's did and if so are they both set the same?

 

[lmcgill97]

Does the viper have the option to chose between RGBM50 and RGBM100 like many of the older suunto's did and if so are they both set the same?

Just checked, they're both set to 100%. Thanks for the suggestion, though.

 

[Diver0001]

Hi! The issue I'm having is making me quite nervous, so I hope you can help. I have two Vyper computers (both purchased used). After a three dive day in July, I downloaded my dives and saw that the download said I went into deco. My computer didn't indicate that in real time during the dive. I deleted and redownloaded the dive, and the NDL times through the profile changed for the same dive and now no deco was indicated. Being worried about this, I wore a computer on each wrist on a recent three dive day and compared them frequently on the third dive. They didn't agree with each other (e.g. one would have a 5 min NDL when the other had 12 min), but neither one showed an ascent time or a ceiling at any point (I was checking them every minute or so). When I downloaded them, both show ascent times and ceilings for a large part of the dive! I have downloaded both computers into DM3 and DM5, and the two versions of DM disagree with each other for the same dive. I'm getting to the point where I don't trust either computer and am tempted to replace them with another brand. Is there any way for me to know what to trust? Thanks! -Lisa
P.S. I just deleted and redownloaded the recent third dive in DM3, and now one computer shows what I saw during the dive (no deco), whereas on the previous download it showed ascent time and a 10 minute ceiling. The other computer still says I was in deco for 20 minutes... I wear both computers on all dives

If they showed the same depth during the dive then you have one of them set to a more conservative setting. IIRC you can get there on the menus by going to Menu->Set->dive->preferences. There are settings for altitude "A" and for how conservative the deco model acts "P". At sea level, the nominal settings are A0 and P0.

R..

 

[miketsp]

It's stated somewhere in the documentation that the real time calculation is based on continuous calculation whereas the subsequent PC calculation depends on the stored samples at whatever rate you specified. So yes, there will be differences in the resulting calculation especially during ascents when the PC will understand that you were deeper on average. It is common to see a deco obligation on the PC even though you didn't incur one during the dive.

 

[Steve_C]

Your dive computers register where the computer is and not where you are. For example slowly going up the anchor line it is easy to quickly raiser your had up above your head. Do that quickly and the too fast ascent light will flash even though you have not changed depth. With computers on two wrists it is easy to have one running one or two feet above the other for most of the dive. In my case my right hand carries a camera and is often lower than my left.