Rounding altitude settings on Cressi Leonardo

[CycleCat]

The altitude settings for my Cressi dive computer are listed in meters in the manual,

Setting zero covers 0-700 meters (2296 feet)
Setting 1 is 700-1500 meters (up to 4921 feet)
Setting 2 is 1500-2400 meters (up to 7874 feet)
Setting 3 is 2400-3700 meters (up to 12139 feet)

To make it easier to remember, do you think it is safe to round these feet up a bit?

I would round setting zero up to 2500 feet
Setting 1 up to 5000 feet
Setting 2 up to 8000 feet
Setting 3 down to 12,000 feet

If I have to strictly follow the meters-to-feet conversion then I'll need to keep a cheat sheet in my dive log!

 

[Esprise Me]

It would be safer to round down than up, I'd think. But if you plan to do a lot of altitude diving, especially if you're going deep enough to come near the NDLs, I'd go with the cheat sheet.

 

[NAM001]

one more reason I like my shearwater

 

[CycleCat]

It would be safer to round down than up, I'd think. But if you plan to do a lot of altitude diving, especially if you're going deep enough to come near the NDLs, I'd go with the cheat sheet.

I live at 7600' and the most popular dive site in NM is at 4600'. But realistically it is probably not much of an issue because 99% of my diving will be at sea level.

 

[ATJ]

I was of the understanding that dive computers actually use the change in pressure for NDL, Deco, tissue, etc. calculations, rather than the depth and so from that perspective the altitude shouldn't matter that much.

Where it does matter is for the depth displayed by the computer. i.e. if the computer thought you were diving at sea level but you were diving at altitude, the depth displayed may be shallower than you actually are. It would only be an issue if you were using the computer in gauge mode and using tables.

I'm happy to be corrected.

 

[Esprise Me]

I was of the understanding that dive computers actually use the change in pressure for NDL, Deco, tissue, etc. calculations, rather than the depth and so from that perspective the altitude shouldn't matter that much.

Where it does matter is for the depth displayed by the computer. i.e. if the computer thought you were diving at sea level but you were diving at altitude, the depth displayed may be shallower than you actually are. It would only be an issue if you were using the computer in gauge mode and using tables.

I'm happy to be corrected.

I'm no expert and also happy to be corrected, but I think you're mistaken. Even if it's true that the algorithm is the same (and I don't think it is--I think it's more conservative), a computer that only miscalculated depth could easily get you bent.

 

[ATJ]

a computer that only miscalculated depth could easily get you bent.

Maybe I didn't explain it right.

I thought the algorithm used the changes in pressure (rather than the depth calculated from the pressure reading). It is the changes in pressure that affect how much nitrogen is absorbed by tissues and how quickly you offgas, not the actual depth. A doubling in pressure is a doubling in pressure regardless of what the assumed depth might be.

Certainly, if you are using tables, depth is all you have, but if the computer uses the pressure (and basically the change in pressure from the start of the dive), the depth is irrelevant.

 

[CycleCat]

This computer stops calculating dive time and pressure on the surface. I guess it needs to know if you are emerging from the water into air that is 13 PSI or 10 PSI.

 

[dmaziuk]

This computer stops calculating dive time and pressure on the surface. I guess it needs to know if you are emerging from the water into air that is 13 PSI or 10 PSI.

Starting pressure, too: it needs to know if you're saturated at 13 or 10 PSI when you hit the water.

My guess is at the Cressi RGBM's level of accuracy rounding by a couple of meters one way or the other shouldn't really matter much (though safe choice is to round down of course), but I gotta ask:

why do you need it in a "round" number of some dead king's shoe sizes?

 

[jborg]

The steps are already a kilometer wide and rounded to metric hundreds, and the actual ambient pressure will vary with weather. I can't imagine rounding a few feet in either direction will make too much of a difference.