Mares M2 Altitude setting

[editmojo]

Just read the M2 manual and it has 4 altitude settings but doesn't explain what that means. Is it a personal setting to tweak the NDL?

moderately clueless,

 

[Greg Barlow]

As you go to higher altitudes, the air pressure decreases from what you would find at sea level. This significantly changes the profile of your dive, as the absolute pressure (atmospheric+water pressure) is different due to the decreased atmospheric portion.

The different settings change the computer's mathematical formula to make the corrections for the decreased atmospheric pressure. I don't have my M2 manual with me, but it likely goes something like this: (this is only a guess, and is surely wrong) Level 0= sea level to 1,000', Level 2=1,000-3,000', Level 3=3,000-5,000'.

Look more closely at your manual, as I am certain it is in there. Try looking at the chart showing the features of the computer, and what each screen demonstrates.

You can also use the altitude settings to make your computer more conservative. For example, the computer might show that at Level 0, you could make a dive to **feet for 40 minutes. At Level 1, it might show a maximum bottom time of 34 minutes at the same depth.

The M2 algorithim is pretty conservative even at the Level 0 setting, but if you have one or more characteristics that would make you more likely to have a DCS hit, then you may wish to make the settings more conservative.

Greg Barlow
Former Science Editor for Rodale's Scuba Diving Magazine

 

[editmojo]

Thanks. I'll do some more reading. Just playing with the simulator mode and shows the behavior you describe.

Just so I understand, The altitude setting assumes surfacing to a lower air pressure thus increasing the risk for DCS so it limits bottom time. Right?

 

[Charlie99]

Just so I understand, The altitude setting assumes surfacing to a lower air pressure thus increasing the risk for DCS so it limits bottom time. Right?

Correct.

More specifically the decompression models have lower limits for the allowable amount of dissolved N2 upon surfacing to the lower air pressure at altitude. The effect of these lowered limits are very close to what you would get by treating your dive as being to a slightly deeper depth.

You will come up with pretty much the same altitude NDL numbers as your computer if you were to assume that the depth was increased 4% per 1,000' of altitude. In other words, the NDL for a 50' dive at 5,000' will be very close to the NDL for a 60' dive at sea level. (5,000' means a 5x4%=20% increase in effective depth. 20% on top of 50' is 60' equivalent sea level depth).

 

[editmojo]

Thanks gentlemen. Always a font of knowledge on SB.