Calculating average depth

[StefinSB]

No... it is

(each depth you were at during the dive) x (time spent at each depth) / total time of dive

Essentially that is how we define the average value of a function. If the function is continuous, we chop the time into tiny bits and the average becomes

average depth = integral of (depth as a function of time dt) / total time

If you were at one depth for half the time and another depth for half the time, then yes... the average depth is just the average of the two depths. But that principle can be generalized (as described above) to any number of depths for any amount of time.

Even better, because pressure is a linear function of depth, and air consumption rate is directly proportional to pressure, after calculating the average depth for any dive, as described here, you can easily calculate your SAC by using:

SAC = (start pressure - end pressure) x [(average depth in feet / 32.8 feet) + 1 ] / time of dive

where the "average depth in feet / 32.8 feet" will give you the pressure, in atm, due to the water.

If your start and end pressures are in psi, and time of your dive is in minutes, you'll get a SAC in psi per minute. You can easily convert this into cubic feet/min by multiplying by

(capacity of your cylinder in cu ft / pressure of your cyl when full in psi)

Or you switch to metric and simply the problem greatly.

 

[dmaziuk]

It is the AI, saying it has SAC rate should have been a clue.

That's the thing about high vs. low-end devices: on the high end you may not need it since it's already tracking you real SAC, but but it's already there from the non-AI version and it's cheaper to just leave it in. Whereas a low-end device may not even have smarts to compute it, and/or UI to show it.

And then you have "instructors" teaching people there's this number that magically appears at a press of a button, and when asked what it is they answer "are you kidding me? ask Shearwater".

 

[tursiops]

It is the AI, saying it has SAC rate should have been a clue.

Yeah, I picked up on that.

 

[tursiops]

And then you have "instructors" teaching people there's this number that magically appears at a press of a button, and when asked what it is they answer "are you kidding me? ask Shearwater".

Are you making this up, or is it something you've witnessed?

 

[dmaziuk]

Are you making this up, or is it something you've witnessed?

Are you joking? Is it a serious question about max depth divided by 2? Surely you understand how to calculate the average depth? If not, you could ask Shearwater or Subsurface, or your 5th grade math teacher.

 

[tursiops]

Dumb retort. Go back to the Pub.

 

[Southpaw57]

Well, I searched here in SB and found a thread where a sample of the TXT file exported from the Cressi Leonardo software is provided:
Sample file from Cressi Leonardo computer?
Here the sample file: https://www.scubaboard.com/community/attachments/leonardo_demo_20110821_1444-txt.191145/
I easily imported it in Excel, and computed the average depth using Excel's AVERAGE function:
View attachment 601873
As you see, the profile is given at increments of 20s (the running time is on row 3) and the depth in m is stored below in row 4.
So making the average of all the depth values gives you an average depth of this profile of 14.57m.
You can find my Excel file here:
http://www.angelofarina.it/Public/Cressi/Leonardo_Demo_20110821_1444.xlsx

That’s awesome, Thank You, seems like a great way to get what I’m looking for right now

 

[jonhall]

I use DiveLog DT on a MacBook and companion Dive Log for iPad/iPhone. Cressi is compatible but must have the download cable for computer - based on I need the cable for my Suunto Cobra. Profile shows average depth. Took a screenshot from software website of what the summary screen looks like on computer - a little dated as the program also includes a button (Summary, Profiles, Details, etc..) for Marine Life. There are different views on the iPad/iPhone. The average depth is shown by a green line across the dive profile.

 

[dmaziuk]

The average depth is shown by a green line across the dive profile.

View attachment 602007

Told you it was half of max depth.

 

[dmaziuk]

That’s awesome, Thank You, seems like a great way to get what I’m looking for right now

Subsurface shows the running average rather that a straight horizontal line:

It will also overlay tank pressure if you enter it: