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ATA vs ATM which is right? Need to know for magazine.

Discussion in 'Basic Scuba Discussions' started by paperdesk, Aug 12, 2008.

  1. paperdesk

    paperdesk Solo Diver

    # of Dives: 100 - 199
    Location: Inchelium, WA
    262
    9
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    Hello! I'm proofreading for a magazine and we have a series of articles about SCUBA diving. The author abbreviated atmospheres as ATM, but I learned it as ATA. I'm wondering if ATM is also correct, or possibly even more correct? Any ideas?

    Thanks!

    Ted
     
  2. Walter

    Walter Instructor, Scuba

    18,583
    321
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    ATM or atm is atmosphere or atmospheres. ATA, ata or ATMA is atmospheres absolute. Both are correct, depending on what you want to say.
     
  3. Sideband

    Sideband Loggerhead Turtle

    # of Dives: 200 - 499
    Location: Carol Stream, IL
    1,514
    3
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    ATM is atmospheres, but ATA is atmospheres Absolute. In other words, 33' of water is 1 ATM of water but it is 2 ATA because of the 1 atmosphere of air above it.
     
  4. paperdesk

    paperdesk Solo Diver

    # of Dives: 100 - 199
    Location: Inchelium, WA
    262
    9
    18
    Hi Walter, thanks for the info. Here is what the article says: "At sea level, the pressure is 1 atmosphere (ATM). at 33 feet below the surface, the pressure is 2 ATM. at 66 feet, it is 3 ATM, and 99 feet it is 4 ATM."

    Is that right, or should it say ATA?
     
    Last edited by a moderator: Aug 12, 2008
  5. roakey

    roakey Old, not bold diver ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Colorado Springs, CO
    3,545
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    As Walter says, depends. If you're talking about relative pressure, it's ATM:

    "For every 33 feet you decend, you increase the pressure by 1 ATM"

    If you're talking about the total pressure, it's ATA:

    "At 66 feet, you're subjected to 3 ATA of pressure".

    Roak

    [added on edit]

    Race, you responded while I was posting. Though both are technically correct, I feel that "ATA" would be more correct in your case.

    Roak
     
  6. Walter

    Walter Instructor, Scuba

    18,583
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    Either is correct, has the concept of atmospheres absolute been introduced? If it has, use ATA, if it hasn't, use ATM. I would replace that w with an s.
     
  7. nwhitney2003

    nwhitney2003 Nassau Grouper

    # of Dives: 25 - 49
    Location: Portland, Oregon
    141
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    I'm wrong so I deleted my post
     
    Last edited: Aug 12, 2008
  8. paperdesk

    paperdesk Solo Diver

    # of Dives: 100 - 199
    Location: Inchelium, WA
    262
    9
    18
    So, IF I understand correctly, the article should list ATA not ATM? It doesn't really explain a lot more about the topic, it's not a technical article.
     
  9. paperdesk

    paperdesk Solo Diver

    # of Dives: 100 - 199
    Location: Inchelium, WA
    262
    9
    18
    Good catch, do you need a job? You can work for us :)
     
  10. Charlie99

    Charlie99 Solo Diver

    # of Dives: 500 - 999
    Location: Silicon Valley, CA / New Bedford, MA / Kihei, Maui
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    ATA is unambigous. It is atmospheres absolute.

    ATM has some possiblity of confusion. Personally, when I use ATM I mean gauge pressure, with sea level atmosphere as the reference. In other words, at 33feet you have a pressure of 1ATM and 2ATA.

    Not everybody uses that convention as the meaning of ATM, but everyone agrees that ATA is an absolute pressure, referenced to vacuum. If you use ATA you eliminate the confusion.
     

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