Changing my computer's altitude setting didn't affect depth measurement?

[boulderjohn]

A computer measures the ambient pressure and converts it to depth for you. It takes the total ATAs, subtracts the air pressure, and multiples by 33 for salt water or 34 for fresh water. Let's see how that equation would calculate depth for 4 atmospheres of pressure (ATA).

In the ocean at sea level:

4 -1 = 3
3 * 33 = 99 feet
​

In fresh water at sea level:

4 - 1 = 3
3 * 34 = 102 feet
​

In fresh water at 2,000 meters/6,600 feet altitude (0.8 ATA)

4 - 0.8 = 3.2
3.2 * 34 = 108.8 feet
​

So, I don't see how 2 identical computers with different altitude settings could give the same depth. If I were to give the computer the benefit of the doubt, I would say that for its decompression readings, it is going off of the ATAs it is measuring but is not translating it to the proper depth for you.

 

[nohappy]

A computer measures the ambient pressure and converts it to depth for you. It takes the total ATAs, subtracts the air pressure, and multiples by 33 for salt water or 34 for fresh water. Let's see how that equation would calculate depth for 4 atmospheres of pressure (ATA).

In the ocean at sea level:

4 -1 = 3
3 * 33 = 99 feet
​

In fresh water at sea level:

4 - 1 = 3
3 * 34 = 102 feet
​

In fresh water at 2,000 meters/6,600 feet altitude (0.8 ATA)

4 - 0.8 = 3.2
3.2 * 34 = 108.8 feet
​

So, I don't see how 2 identical computers with different altitude settings could give the same depth. If I were to give the computer the benefit of the doubt, I would say that for its decompression readings, it is going off of the ATAs it is measuring but is not translating it to the proper depth for you.

Thank you! That is exactly my question, not to mention it probably should consider fresh water. My computer probably should not give me exact same depth if it has 0.1m precision.

 

[dmaziuk]

That's in the manual too: it's set for salt with no adjustment. "Fresh water depths are about 3% lower".

 

[dmaziuk]

The computers read altitude automatically, so if the computer was on when you entered the water, it would know you were ta altitude. If the computer turned on automatically after you began your descent, it would assume you were at sea level.

Leonardo does not read the altitude automatically, you set it in the menu. I bet the setting does not affect the depth display, it reads as if you were at sea level anyway.

 

[boulderjohn]

Leonardo does not read the altitude automatically, you set it in the menu. I bet the setting does not affect the depth display, it reads as if you were at sea level anyway.

Check the context. I was talking about Shearwater computers in that sentence.

 

[Bob DBF]

So, I don't see how 2 identical computers with different altitude settings could give the same depth. If I were to give the computer the benefit of the doubt, I would say that for its decompression readings, it is going off of the ATAs it is measuring but is not translating it to the proper depth for you.

It would depend on whether the "altitude setting" is for conservatism, at that point it could imput the altitude into the algorithm without changing the depth display as your actual physical altitude has not changed. If the altitude actually changes, the computer would change the depth display and altitude in the computer. That is the understanding I have of my computer, and it seems to operate that way when I use it. The conservatism setting just spoofs altitude so you can understand and quantify the change for your diving.


Bob

 

[nohappy]

It would depend on whether the "altitude setting" is for conservatism, at that point it could imput the altitude into the algorithm without changing the depth display as your actual physical altitude has not changed. If the altitude actually changes, the computer would change the depth display and altitude in the computer. That is the understanding I have of my computer, and it seems to operate that way when I use it. The conservatism setting just spoofs altitude so you can understand and quantify the change for your diving.


Bob

Thank you @Bob DBF , I'd like to think that way too. But here comes other questions, if my computer is able to sense altitude -
1. Then I believe Cressi would like to mention that feature in the manual/spec.
2. Then I should not need to set altitude setting since it can automatically sense altitude ( keep in mind that it chose to believe the altitude it detected instead of my configuration)

If it can't detect air pressure (for altitude), another reasonable explanation could be that it save the ambient pressure at the start point (the moment I started to descent) and make that ambient pressure as offset.

 

[Bob DBF]

Thank you @Bob DBF , I'd like to think that way too. But here comes other questions, if my computer is able to sense altitude -
1. Then I believe Cressi would like to mention that feature in the manual/spec.
2. Then I should not need to set altitude setting since it can automatically sense altitude ( keep in mind that it chose to believe the altitude it detected instead of my configuration)

If it can't detect air pressure (for altitude), another reasonable explanation could be that it save the ambient pressure at the start point (the moment I started to descent) and make that ambient pressure as offset.

If the computer does not say it adjusts to altitude then it dosent. Reread the manual as sometimes it is easy to miss a small detail, not that that is a small detail.

I know how the two I have owned work, and that makes me no kind of expert. If your computer manually sets to altitude, I would guess they figure the depth is close enough and the algorithm will cover it.


Bob

 

[dmaziuk]

If your computer manually sets to altitude, I would guess they figure the depth is close enough and the algorithm will cover it.

Depth doesn't change, a hundred feet at thousand feet elevation is still a hundred feet. Only off-gassing fudge factor changes.

 

[dmaziuk]

Check the context. I was talking about Shearwater computers in that sentence.

Yes, and OP asked about a Leonardo. Which I happen to own.