Depth calibration on Oceanic dive computers

[Divin'Papaw]

Is the depth sensor on Oceanic computers calibrated for freshwater or saltwater?

 

[Shark Bate]

Is the depth sensor on Oceanic computers calibrated for freshwater or saltwater?

I have two Oceanic computers and both of them use salt water depth calculations, but the units will automatically switch over to fresh water depth calibration when the altitude sensor indicates that the unit is at 2,000 ft or higher.

I assume since my Datamask and Atom 2 both do the same thing (that info directly from manual) that all the Oceanic computers would be similar, at least the newer models.

I know from using older Uwatec computers that they used fresh water so when I was ocean diving I was always a couple feet off on depth - always thought that was a bit lame even tho they are great computers - I like the system described above that Oceanic uses a lot better - even tho it really doesn't make a ton of difference if you're only off by a couple feet.

 

[Doug Krause]

2,000 calibration switch is correct, and has been on all units produced in the last 15+ years.

Thanks for jumping in Shark Bate.

 

[Shark Bate]

Can you tell it's a SLOW day for me ;+)

 

[Divin'Papaw]

What about us freshwater divers in the Midwest? Not that big of a deal, but it would sure be nice to eventually see a user accessible setting. I did two quarry dives yesterday and my computer said 116' and my Uwatec bottom timer (which is set to freshwater) said 121' and 120'.

It doesn't make that much difference until you're deeper than 100' or so, but then it starts to add up.

 

[Hoosier]

Interesting...

My Aeris com.:88ft max.
Sensus Ultra: 82ft max
OMS BT: 88ft max.

Huh~~ Sensus ???????

 

[Charlie99]

What about us freshwater divers in the Midwest? Not that big of a deal, but it would sure be nice to eventually see a user accessible setting. I did two quarry dives yesterday and my computer said 116' and my Uwatec bottom timer (which is set to freshwater) said 121' and 120'.

It doesn't make that much difference until you're deeper than 100' or so, but then it starts to add up.

Dive tables are typically in fsw, not ffw, so IMO it makes more sense to have gauges that read the same as your table -- fsw.

Changing between ffw and fsw won't change the internal decomression calculations of the computer, just as changing to meters doesn't change them.

An aside to Doug Krause -- Oceanic computer aren't all the accurate on altitude measurement and it's not obvious whether the computer has chosen to display ffw or fsw when around 2000' of altitude. It would be nice to have an indicator as to which depth unit is being used --- msw, mfw, ffw, or fsw.

 

[Shark Bate]

What about us freshwater divers in the Midwest? Not that big of a deal, but it would sure be nice to eventually see a user accessible setting. I did two quarry dives yesterday and my computer said 116' and my Uwatec bottom timer (which is set to freshwater) said 121' and 120'.

It doesn't make that much difference until you're deeper than 100' or so, but then it starts to add up.

You're six feet tall - so in my book everything is OK

Just remember to give your lower legs and feet a couple more minutes at the safety stop ;+)

 

[Divin'Papaw]

I'm not concerned from an NDL perspective. I was wanting to confirm what was behind the difference in my computer and BT. I suspected it was that one was measuring ffw and the other fsw, especially when I noticed that the difference increased relative to depth. Call it curiosity.

 

[Shark Bate]

I did some checking on water densities - - looks like salt water is about 3.5% more dense than fresh (on average) so at 100 feet the difference should only be about 3.5 feet. I suspect the larger difference you are showing is due to some small instrument error.

Still it's not sufficient enough to really make a substantial difference - computers are just using averages and algorithms, so there is always a little "fudge" factor involved anyway.