Petrel average depth calculation

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insomnia

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Hello,

Can someone explain me how is the average depth calculated on Petrel?

Many thanks!

btw. Do you plan to include list of mandatory deco stops in new Petrel firmware? It would be nice to see complete list of all deco stops and not just the first deco stop. I guess there is no chance to add a feature to ON/OFF deep stops in the future?
 
manual (page 16) states: "Displays the average depth of the current dive, updated once per second".

following that statement, one would think it's the summation of the values of the samples (each recorded current depth)/number of samples (total time in seconds of the dive)...

Are you finding a potential error?
 
It would be nice to see complete list of all deco stops and not just the first deco stop.

You really should know exactly what stops you are going to make before you even begin a decompression dive, and ideally, they should be written on your fins... the first stop and TTS should only be a visual confirmation that you are following the plan.

I guess there is no chance to add a feature to ON/OFF deep stops in the future?

AFAIK, that feature already exists, it is the gradient factor.

 
btw. Do you plan to include list of mandatory deco stops in new Petrel firmware? It would be nice to see complete list of all deco stops and not just the first deco stop.

That's something you would know in advance from preplanning the dive. The nice thing about the Petrel, and computers like it, is that the deco models they use are readily available on your compute/tablet/smartphone.
 
manual (page 16) states: "Displays the average depth of the current dive, updated once per second".

following that statement, one would think it's the summation of the values of the samples (each recorded current depth)/number of samples (total time in seconds of the dive)...

Are you finding a potential error?

I have gone thru manual x times. I just wanted to know if it is weighted average or not.

You really should know exactly what stops you are going to make before you even begin a decompression dive, and ideally, they should be written on your fins... the first stop and TTS should only be a visual confirmation that you are following the plan.



AFAIK, that feature already exists, it is the gradient factor.


Yes, everybody should know but why not to have a visual confirmation of all deco stops?

I know some computers which are working w/ GF and give you possibility to ON/OFF deep stops.
 
I know some computers which are working w/ GF and give you possibility to ON/OFF deep stops.

AFAIK, gradient factors were introduced, among other reasons, to apply the desired degree of conservatism consistently throughout the entire ascent and deco. Adding arbitrary deep stops based on a heuristic, on top of those already generated by GF, defeats the purpose by effectively undoing some of what GF was designed to achieve in the first place. If you want more deeper stops, you can simply reduce GF to slow down ascent, and it will at least be a way of introducing more conservatism to the dive that has some sort of a scientific backing.

Besides that, there is also a sound engineering principle that says you should not have 2 knobs to control the same thing. GF is a single knob to control conservatism in an elegant manner, an ON/OFF deep stop would be effectively doing the same, at which point you might want to start asking yourself whether you should be using one or the other, and what it means to use both...
 
Yes, everybody should know but why not to have a visual confirmation of all deco stops?

I know some computers which are working w/ GF and give you possibility to ON/OFF deep stops.

The only stop that is completely calculated (real?) is the stop your on; the subsequent stops are all affected by whatever you do next. In reality, the computer expects you to ascend and make gas switches based on what you've told it is available, but it can't possibly know *if* you'll actually stay on plan, if/when you'll make the gas switches, if/when/how lost gas is handled, or if you'll program another gas in real time. You'll discover the Petrel provides TTS and an @+5 calculation which is a forecast.

I believe seeing an updated schedule would do nothing more than provide confusing information. You have TTS, Stop Depth & Time, and @+5 TTS... I ask myself, what more do you need and how would you apply it?? The key point here is decompression dives are structured, which means I don't need an iterative and constantly updating schedule because I already have it on paper before I enter the water. The computer does serve to prove meaningful information in the event I overstay or have to do something outside of the plan, etc. But at a certain point, I have exactly the resources I have available, and the computer is unlikely to affect that outcome.
 
Thank you all for your contribution.

Can we get back to my main question which was how average depth is being calculated on Petrel?

---------- Post added June 18th, 2014 at 07:01 PM ----------

My Petrel is in surface mode now as I am 10 days after my last dive. It shows max depth 42m and average depth 21m, so it seems to me that it is not weighted average but just max depth divided by 2.
 
I exported a dive from my Petral to a spreadsheet, and using the average function on the data set (excluding the first value and the last zero values), the math came within tenths of what the log showed... (the exported data is in 10 second intervals vs. 1 second stated that the processor is doing)

apparently just "pure" number crunching as I suspected, no weighted average...

the data, however, was a fairly constant changing data set, as it was a calibration test on the unit.

try it with some of your data, and see if you get the same results....
 
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Please, dont take me wrong and excuse my english as I am not from english speaking country. I do understand and agree w/ what guys wrote - that is just it.

I will try to export my logged dive to CSV and will try to check this in Excel.

---------- Post added June 18th, 2014 at 08:42 PM ----------

Well it seems it is weighted average based on my analysis in Excel. Strange thing is that Petrel shows different average depth in compare to Shearwater Desktop ?!
 
https://www.shearwater.com/products/swift/

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