Q re: N2 loading bar on Peregrine

[melliodora]

Response from Shearwater:

"I'll review that definition in the manual with other members of our team to see if it is the best way to word it when it does simply say "it is full once decompression stops will be needed".

The N₂ bar is designed to give you a quick visual of your overall nitrogen loading. It’s scaled conservatively, so it can show full even when you still have no-stop time left. It’s not an indication of a problem with your computer or settings, and just a reminder that you’re near the upper end of your NDL range.

Because it’s a broad, summarized, and conservative overview, the N₂ bar can show as full even when your detailed Tissue Bar Graph still displays compartments in green or yellow. That tissue screen gives the more accurate picture of nitrogen loading in different compartments, and the fact that those remain green or yellow confirms that you’re well within safe limits, even when the mainscreen N₂ bar looks full.

You’re interpreting your dive data carefully, and that’s great to see especially after your DCS experience. The behaviour you’re seeing is expected. I understand the confusion though and I'm sharing your email with other members of our team for review of its wording."

 

[johndiver999]

I always read about how these computers are a "must have" and then when I read that a bar graph that shows loading does not really show loading - in the simplest terms possible, I'm confused.

Why would they make a bar graph that does not represent EXACTLY what someone would expect it to do?

I use much simpler and older oceanic computers (with one button) and they have a bar graph that fills up and shows very clearly when you go from no deco to deco. It is a nice sanity check when you glance at the computer and perhaps when you are a little narced, distracted, cold or stressed.

 

[David Carron]

I always read about how these computers are a "must have" and then when I read that a bar graph that shows loading does not really show loading - in the simplest terms possible, I'm confused.

Why would they make a bar graph that does not represent EXACTLY what someone would expect it to do?

Probably because no two people have the same expectations and also because if you were to look closely you'd notice that the really isn't 'one true definition"

Personally, I've never implemented anything like this because I'd rather have no information than potentially misleading information.

Edit. After a bit of thought, the current loading divided by (gf hi times m0) for that tissue seems to me like the most plausible definition for a "nitrogen loading bargraph" but Im sure that other people would have other definitions: a bar showing GFsurf divided by GFhi would probably be just as good.

 

[melliodora]

I also question the use for this particular bar, as opposed to the tissue compartment one, but I get everything I need (as a rec diver) from monitoring a combination of NDL, GF99 and SfGF. I was just confused when this visual graph seemed at odds with those. I agree having it *almost* full when you are approaching your NDL (or are still near your GFHi even if NDL back up) would be more helpful though

 

[melliodora]

Personally, I've never implemented anything like this because I'd rather have no information than potentially misleading information.

Agree - although this graph is fixed to the main screen, not an option to not display it.

 

[TravisD]

A tiny bar-graph will never indicate *anything* exactly.

Why would they make a bar graph that does not represent EXACTLY what someone would expect it to do?

A tiny bar graph is probably the least accurate way of displaying a value for anything, in any circumstance. At best its a quick reference - to many the Color is probably more useful, but that doesn't work for everyone (at least not something using Red and Green). Combine this with imprecise data feeding it, based on inexact science - the tolerances are stacking up to be "Hey, this icon looks like I should start thinking about heading up" more than "Here's an accurate measurement of my N2 loading that I can plug into the algorithm running in my head". It's estimates all the way down.

 

[inquis]

A tiny bar-graph will never indicate *anything* exactly.

Sure, but it shouldn't cause confusion by conflicting with other information provided.

 

[melliodora]

@TravisD true - but as Shearwater acknowledged, it's the way that it's described in the manual that contradicts what it actually shows (red does not = deco). For me at least, it has also shown full/red when I have ~20 mins NDL, then stayed red until I surface (even if GF99 has been >0/"on" for some time. Personally, given this response from Shearwater and the fact that I am now monitoring GF99/SfGF, I feel like I will just ignore this graph entirely, which isn't great for something built into the home screen of my computer and that should have some purpose

 

[johndiver999]

A tiny bar-graph will never indicate *anything* exactly.


A tiny bar graph is probably the least accurate way of displaying a value for anything, in any circumstance. At best its a quick reference - to many the Color is probably more useful, but that doesn't work for everyone (at least not something using Red and Green). Combine this with imprecise data feeding it, based on inexact science - the tolerances are stacking up to be "Hey, this icon looks like I should start thinking about heading up" more than "Here's an accurate measurement of my N2 loading that I can plug into the algorithm running in my head". It's estimates all the way down.

That is a ridiculous statement. It is 100% perfectly accurate, why would you assume it is anything other?

As for the color, perhaps it has some utility, but for people who are color blind and have issues with green/red a simple bar graph should work.

 

[melliodora]

My interpretation of that statement about accuracy was that 1) it's not a bar graph in the true sense of the word (no axes and more importantly no scale 2) a bar graph really only tells you one value and that's the top value, and here there is confusion/contradiction as to what that top value (full bar) actually means, as it doesn't mean what it says in the manual and 3) it's tiny, so pretty hard to read specifics, especially underwater