Hello and welcome to our community! Is this your first visit?
Register
Results 1 to 10 of 10
  1. #1
    Established TDF Member
    Join Date
    Apr 2017
    Location
    Glossop
    Posts
    558
    Likes (Given)
    205
    Likes (Received)
    163

    Shearwater plus altitude

    Does anyone know if the SW GF adjusts automatically for altitude?

    Dives will be at around 350m so hardly a massive change but just curious.

  2. #2
    TDF Member
    Join Date
    Jan 2013
    Location
    South of France
    Posts
    364
    Likes (Given)
    87
    Likes (Received)
    85
    I'm not aware of any algorithm - or indeed theoretical or experimental justification - for adjusting gradient factors as a function of surface pressure, and it seems unlikely that shearwater would have just made one up.

    The effects of diver saturation level wrt to surface pressure are probably not to be sniffed at though; I live at 660m and can find myself on-gassing at sea-level three hours after leaving home.



    Quote Originally Posted by JonG View Post
    Does anyone know if the SW GF adjusts automatically for altitude?

    Dives will be at around 350m so hardly a massive change but just curious.

  3. #3
    Established TDF Member
    Join Date
    Apr 2017
    Location
    Glossop
    Posts
    558
    Likes (Given)
    205
    Likes (Received)
    163
    Sorry it's a GF computer not looking to adjust actual GF for the dive just wondered if the pressure sensor in the SW compensated for the altitude

  4. #4
    TDF Member
    Join Date
    Jan 2013
    Location
    South of France
    Posts
    364
    Likes (Given)
    87
    Likes (Received)
    85
    As far as I'm aware the shearwater computers continuously monitor ambient pressure. This means that they know the diver's initial tissue saturation and dive surface pressure and can take both into account.
    Last edited by shapeshifter; 02-12-2018 at 11:49 AM.

  5. #5
    Where'd The Bubbles Go ....? Capt Morgan's Avatar
    Join Date
    Dec 2012
    Location
    The Land Of the Black Stuff
    Posts
    1,807
    Likes (Given)
    1239
    Likes (Received)
    1158
    I only have experience with the Petrel and it has the option to set the altitude to auto and it compensates for changes in pressure/altitude.
    The default for this setting is sea level so would need checked to ensure it's set to auto, that's if the GF has the feature.
    Last edited by Capt Morgan; 02-12-2018 at 12:44 PM.

  6. #6
    Established TDF Member
    Join Date
    May 2014
    Location
    Colchester
    Posts
    1,280
    Likes (Given)
    1690
    Likes (Received)
    309
    Quote Originally Posted by JonG View Post
    Does anyone know if the SW GF adjusts automatically for altitude?

    Dives will be at around 350m so hardly a massive change but just curious.
    As I understand it, it's not the GF that would need adjustment for diving at altitude - it's the m-value.

    The m-value your profile is going to follow will need to take into account the lower ambient pressure at the surface - i.e. it should anticipate your surfacing AP from the AP it recorded at the start of your dive. After that, it's just about tracking half times during SI. The GF wouldn't change, as it's there to give you a conservative offset from whatever m-value your algo has figured for your executed profile.

    To my knowledge, this is done as standard by any reasonably modern computer.

  7. #7
    Established TDF Member
    Join Date
    Oct 2015
    Location
    West Lothian
    Posts
    1,409
    Likes (Given)
    460
    Likes (Received)
    434
    Quote Originally Posted by PhilPage View Post
    As I understand it, it's not the GF that would need adjustment for diving at altitude - it's the m-value.

    The m-value your profile is going to follow will need to take into account the lower ambient pressure at the surface - i.e. it should anticipate your surfacing AP from the AP it recorded at the start of your dive. After that, it's just about tracking half times during SI. The GF wouldn't change, as it's there to give you a conservative offset from whatever m-value your algo has figured for your executed profile.

    To my knowledge, this is done as standard by any reasonably modern computer.
    I think that depends on the algorithm employed by the computer. I am sure that some do not adjust unless it is outwith a certain parameter.

  8. #8
    Established TDF Member
    Join Date
    Apr 2017
    Location
    Glossop
    Posts
    558
    Likes (Given)
    205
    Likes (Received)
    163
    Just for clarity when I said "SW GF" I meant the Shearwater Gradient Factor model of computer (like Perdix, Predator etc.) its a bit dated but still works.

    I am not thinking the actual GF needs changing buyt as Neil says some computers compensate, others need a change to a parameter, there is no parameter to change so wondered if it would auto correct.

  9. #9
    TDF Member
    Join Date
    Jan 2013
    Location
    South of France
    Posts
    364
    Likes (Given)
    87
    Likes (Received)
    85
    All of the ZHL algorithms automatically and implicitly compensate for dives at altitude by taking the dive surface pressure as a reference and calculating with respect to that.

    Some computers however don't measure surface pressure and make you manually set it instead.

  10. #10
    Established TDF Member MikeF's Avatar
    Join Date
    Dec 2012
    Location
    Darkest Aberdeenshire
    Posts
    3,643
    Likes (Given)
    191
    Likes (Received)
    2581
    drop an email to shearwater? the manual is still up on the website but doesn't seem to mention barometric pressure


 

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •