Calculating average depth

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since it is a serious question then here is an example. you make a dive to 100 ft for 2 minutes and the rest of the dive is at 30' for 60 minutes) you have to calculate it as depth minutes in this case 2*100 + 60*30 and then get 2000. divide the the 2000 by num of minutes ( 62 ) ang get 32 as an avg depth for consumption rate.

That’s a great explanation, thanks everyone for being patient with the new guy
 
I started with a Cressi Leonardo and can confirm you need to buy the cable and download the dives to get your average depth, and then you can find it in Subsurface. I could never get Cressi's software to work on any of my computers. I would also caution you that the Leonardo only retains data for the last 60 dives, so you need to download them regularly to avoid losing that data. I'll shut up before I start fangirling over my Teric that not only exports data over Bluetooth but tells me my average depth and SAC right on the screen, along with a graph of my dive...
 
Mathematically the average depth is defined as the ratio of the integral of instaneous depth along the diving time, divided the total diving time.
This can be approximated quite accurately by a numerical summation, if depth is stored every second.
Just sum all the depth values along the dive profile and divid by the number of values.
This is less accurate if depth is stored every minute instead of every second, but still it can give a reasonable approximation.
 
I started with a Cressi Leonardo and can confirm you need to buy the cable and download the dives to get your average depth, and then you can find it in Subsurface. I could never get Cressi's software to work on any of my computers. I would also caution you that the Leonardo only retains data for the last 60 dives, so you need to download them regularly to avoid losing that data. I'll shut up before I start fangirling over my Teric that not only exports data over Bluetooth but tells me my average depth and SAC right on the screen, along with a graph of my dive...
Yeah, but I paid 99 eur for my Leonardo. A Teric would cost 10 times more..
 
Your gas consumption is SAC times pressure times dive time. Are you spending your entire dive time at "average" pressure on a square profile? How about a triangular one? A see-saw?

I just don't get the notion of "average depth" -- is it max depth divided by 2? -- so I find its lack not odd at all.

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)
 

The example in that page talks about five bowls and their depths. So they add the five depths and divide by five.

That's okay if you have five bowls. But when diving, we are calculating a time averaged depth.

Which means instead of bowls, we have... time.

So yes, it is the same thing... just substitute "time" for the "bowls".

How much time do you have on a dive? If you have, for example, 40 minutes then you would take the depth for each minute, add them together, and divide by 40 to get the average depth.

Just like how they took the depth for each of the 5 "bowls", added them, and divided by 5 to get the average depth.
 
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:
Cressi.png

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
 
Average depth = a few button pushes on my Perdix, one or two pushes before the SAC rate :D

Should've paid an extra $80 for Perdix AI that tracks and logs your actual gas mileage, no average depth required.
 
https://www.shearwater.com/products/peregrine/

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