Reset of Average Depth

[R.Chisholm]

Hi,

I own a Petrel 3 and would like to reset the average depth once I reach my target depth.

I'm using the v98/BT11 version of the firmware and this feature only seems to be enabled in Gauge Mode.

I have noticed that other Shearwater computers such as the Perdix seem to have this feature available in other modes i.e. OC TEC - not sure which version of the firmware this was on & I'd like to be able to do the same on my Petrel 3.

Is there any way of doing this with the Petrel 3 using the latest firmware version?

 

[LFMarm]

I don’t know the answer, but I’m genuinely curious—what’s the rationale for resetting the average depth at that point in the dive?

 

[inquis]

what’s the rationale for resetting the average depth at that point in the dive?

No idea as to the OP's rational, but I've done it to benchmark a section of the dive for consumption calculations made during the SI (class setting). I can also see it being useful to characterize a certain area of the dive (e.g., an up & down cave section), excluding other parts of the dive that would skew the avg depth. Again, consumption might be the relevant context.

That said, all this can be done in a dive log program like Subsurface later on. Doing it on the dive computer directly just saves a bit of time in some cases.

 

[sea_otter]

The option to reset average depth was originally included in all modes (by mistake), but this was fixed in v65. It is currently only present in gauge mode.

As to why, it is a helpful way to add some conservatism to your deco planning if you're diving in gauge mode and using average depth to calculate ndl/deco, but I'm not sure why you'd want it in computer mode.


From https://www.shearwater.cz/soubor-petrel2-perdixai-perdix-nerd-2-v65-release-notes-6-.pdf
FIX (All models): Removed “Reset Average Depth” menu option in non-gauge modes(was appearing if the Timer was added to the main screen).

 

[LFMarm]

No idea as to the OP's rational, but I've done it to benchmark a section of the dive for consumption calculations made during the SI (class setting). I can also see it being useful to characterize a certain area of the dive (e.g., an up & down cave section), excluding other parts of the dive that would skew the avg depth. Again, consumption might be the relevant context.

That said, all this can be done in a dive log program like Subsurface later on. Doing it on the dive computer directly just saves a bit of time in some cases.

Never thought about it because I like to do it on the dive log afterwards.

 

[R.Chisholm]

I don’t know the answer, but I’m genuinely curious—what’s the rationale for resetting the average depth at that point in the dive?

Hi,

Our pre-computed deco profile is primarily driven by bottom time and average bottom depth - the descent itself at least to the depths I am going is probably still within NDL.

I'd therefore like to know the average depth from the point where we arrived at target depth to the point we initiated the ascent.

This will allow me to have some idea of what the actual decompression profile is going to look like for each of the divers in the team without guessing at each deco stop if each diver is happy to ascend to the next stop.

To illustrate this - lets say we are diving with 4 divers in 2 teams of 2. We computed and possibly linearised the deco profile for a dive to 45m average depth with 20 minutes bottom time using Tx 21/35 as back gas and deco with NX 50 starting at 21m. We agree to to the ascent together and aim to surface at the same time when everyone has completed their decompression.

One of the two teams went a little deeper and ended up with an average depth of 48m for the bottom part of the dive. If I am told this I will know I should expect about 5 minutes extra deco time split between the 9m and the 6m stop (if 6m is the final stop).

I realise there are alternatives - i.e. putting the computer in to gauge mode or having everyone do their stop at an individual depth based on the recommendations of their computer or asking every diver if they are happy to head to the next stop at every stop.

Still - it would be useful to know the average depth from arriving at target depth to initiating the ascent on the shot line for the diver leading the ascent.

Worth noting that the overall average depth including the descent let alone the average after switching at 21m to the deco gas is less useful in terms of predicting potential adjustments to the pre-planned deco profile.

 

[inquis]

Still - it would be useful to know the average depth from arriving at target depth to initiating the ascent on the shot line

You could inflate the overall average by half the descent proportion. It's not exact, but will be close for the likely small proportion. If descent was 3 mins and ascent occurred at 30 min runtime, the descent was 10% of the time, so inflate by 5%. For a 100 ft bottom depth, the overall average would be 95 ft. 5% is 4.75, so darn close to 100 ft after inflation.