What makes a watch 70,000 a/m rated?
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  1. #1
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    What makes a watch 70,000 a/m rated?

    The new Omega Seamaster Aqua Terra is rated to 15,000 gauss based on new materials used in the movement.

    Others movements are encased in soft iron including the extra thick dial making them achieve the rating e.g the PRS2 Dreadnought to 30,000 a/m and the Kobold Seal to 80,000. I happen to know as I own a case cracker.

    I believe watches use steel alloy balance springs to avoid their magnetizing.

    I have a watch that is stamped 70,000 a/m.

    I don't believe it is.

    It is a steel case, I assume 316L. It has a 'normal' thickness dial made of a copper colored metal. The bog standard Miyota 9015. It was $400 shipped new, so no special alloys in the steel or modifications to the movement and the movement holder is exactly that, not a special magnetic deflecting piece of metal. No movement cover, just a regular back.

    I have emailed the company to ask, but no reply which is odd as pre and post- sale communication was immediate.

    I like and wear the watch daily, so I am not particularly perturbed, more wondering.

    Thought or comments?
    Last edited by robert67; August 4th, 2014 at 04:12.

  2. #2
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    Re: What makes a watch 70,000 a/m rated?

    Here's how Damasko does it (from watchmann.com):

    The Magnetic Field Protection - The Case inside the Case


    Every Damasko watch features an important technical detail which is not visible at first sight but has a major influence on its accuracy under harsh conditions – the anti-magnetic cage.
    Only very few mechanical pilot’s watches are equipped with this feature. The unique inner case consists of the dial, the movement retaining ring, and a second back. These parts are made of a special material with anti-magnetic characteristics which is able to withstand magnetic fields with a strength up to 80,000 A/m. They are machined with maximum precision to ensure an exact fit and to prevent the escapement from being magnetically charged.
    The magnetic field protection in combination with martensitic ice-hardened steel is patented.

  3. #3
    Member geoffbot's Avatar
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    Re: What makes a watch 70,000 a/m rated?

    I think you should test it
    Henry Krinkle likes this.

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  5. #4
    Moderator Public Forum John MS's Avatar
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    Re: What makes a watch 70,000 a/m rated?

    Quote Originally Posted by robert67 View Post
    The new Omega Seamaster Aqua Terra is rated to 15,000 gauss based on new materials used in the movement.

    Others movements are encased in soft iron including the extra thick dial making them achieve the rating e.g the PRS2 Dreadnought to 30,000 a/m and the Kobold Seal to 80,000. I happen to know as I own a case cracker.

    I believe watches use steel alloy balance springs to avoid their magnetizing.

    I have a watch that is stamped 70,000 a/m.

    I don't believe it is.

    It is a steel case, I assume 316L. It has a 'normal' thickness dial made of a copper colored metal. The bog standard Miyota 9015. It was $400 shipped new, so no special alloys in the steel or modifications to the movement and the movement holder is exactly that, not a special magnetic deflecting piece of metal. No movement cover, just a regular back.

    I have emailed the company to ask, but no reply which is odd as pre and post- sale communication was immediate.

    I like and wear the watch daily, so I am not particularly perturbed, more wondering.

    Thought or comments?
    I guess the real question is how do you determine whether the rating a manufacturer stamps on the dial is reliable. The rating could be 70,000 gauss for anti-magnetic or 10,000 meters for depth. Because none of us have the equipment to perform such testing it really comes down to confidence in the makers reputation.

    Compare what you paid for the unidentified watch and the quality of components like the movement to anti-magnetic watches from recognized watch makers. Is the rating well beyond that found on most anti-magnetic watches? I think the answer to your question is obvious.
    Last edited by John MS; August 4th, 2014 at 16:05.

  6. #5
    Member umarrajs's Avatar
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    Re: What makes a watch 70,000 a/m rated?

    Yes, curious about this.
    A few relatively inexpensive watches come to mind that have 70,000 A/m rating:

    1. Deep Blue Master 2000 GMT Diver
    2. Helson Shark Diver Bronze 45mm
    3. Armida A6

    Deep blue and Helson have standard ETA 2836 and 2824 respectively while Armida uses Miyota 9015. So the anti-magnetism is most likely achieved by housing the entire movement into a case made of a highly conductive (permeable) material and/or additionally encasing the movement in soft-iron clasp to prevent the forming of magnetic fields inside the watch itself.

    So question is: How much anti-magnetism can be achieved by introducing a Faraday Cage?

  7. #6
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    Re: What makes a watch 70,000 a/m rated?

    Quote Originally Posted by John MS View Post

    Is the rating well beyond that found on most anti-magnetic watches? I think the answer to your question is obvious.
    I think it is obvious. Since most watches with a high a/m rating have the movement enclosed in an inner case of anti-magnetic material, and mine doesn't, how can it have that 70,000 a/m rating!

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