Omega Cal. 2500: precision timekeeping

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  1. #1
    Member Francois Boucher's Avatar
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    Omega Cal. 2500: precision timekeeping

    I've had my Omega Planet Ocean (2201-50-00) for three weeks now, and wearing it almost continuously since it arrived. In that time, the watch gained three seconds.

    I am very impressed by the precision timekeeping of this watch.

    I have another 2500 ticking inside the Aqua Terra I bought three years ago. This is also an excellent instrument, gaining approximately 2 seconds per week.

    I have two comments/questions about this:

    1. I wonder whether George Daniel's coaxial escapement (coupled or not with Omega's free-sprung balance) has ever been compared with the Tourbillon (invented by L.A. Breguet, 1795) in terms of precision. Do people here have an opinion about which is the better technology in terms of precision, and maybe other characteristics such as sturdiness, difficulty of execution or maintenance?

    2. This is more of a theoretical question (...because it surely won't happen): shouldn't COSC redefine their criteria for chronometer certification in the XXI Century, with the amazing technological devellopments that we are seeing in watchmaking?

    François
    Last edited by Francois Boucher; September 23rd, 2006 at 00:37.
    François – Quebec City, QC

  2. #2
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    Re: Omega Cal. 2500: precision timekeeping

    Quote Originally Posted by Francois Boucher
    1. I wonder whether George Daniel's coaxial escapement (coupled or not with Omega's free-sprung balance) has ever been compared with the Tourbillon (invented by L.A. Breguet, 1795) in terms of precision.
    Probably not, because they achieve different things, and AFAIK the Daniels escapement doesn't have anything to do with accuracy, more to do with efficiency through lower friction (it would be rather like comparing fuel injection with a limited slip differential).
    Do people here have an opinion about which is the better technology in terms of precision, and maybe other characteristics such as sturdiness, difficulty of execution or maintenance?
    Well these are not subtitute technologies - it is possible to have a watch with both types, for example - so cannot be compared in those terms. In "bang for the buck" terms, the escapement increases the cost of a (for example) Omega watch by around 50%, power reserve by around 5%, and servicing lengths by an unknown amount since the oldest Omegas with this escapement are I think still only about 5-6 years old). A tourbillon increases the cost many times over, increases accuracy, increases the servicing requirements, but also - partly because of the sheer cost - changes the positioning of the watch in the market completely. This sounds pretty even to me.

    In terms of what's relevant to the typical watch buyer, neither seems to have much to offer, IMHO. The tourbillon is probably more interesting to a layman, not least because in most watches so equipped, you can actually see it.
    2. This is more of a theoretical question (...because it surely won't happen): shouldn't COSC redefine their criteria for chronometer certification in the XXI Century, with the amazing technological devellopments that we are seeing in watchmaking?
    Yes, I think some sort of tighter definition of a "chronometer" would be useful, but I do broadly understand the reasons why COSC won't change.
    Last edited by publandlord; September 23rd, 2006 at 14:56.

  3. #3
    Member Francois Boucher's Avatar
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    Omega Cal. 2500: isochronism and accuracy

    I really appreciate your thoughtful answer to my initial post.

    However, I want to explore the issue of accuracy further.

    I'm not a mechanical engineer, nor a watchmaker. But I figure that if the coaxial escapement decreases friction in the system, it must also increase isochronism by incrementally reducing dynamic and positional friction, and thus, irregularities in the movement of the anchor and balance amplitude.

    It seems to me that Walt Odets is saying as much in his review of the coaxial escapement in the Horologium:

    In small calibers like the Omega, the co-axial escapement is aimed much more at stability over time than "accuracy" per se. As delivered from the factory, the Omega Co-Axial appeared to provide consistent rate, and was adjusted about 15 seconds a day fast. Positional performance was essentially perfect.

    Timer tapes for dial-up and crown-down positions are shown left after a rate adjustment (1) with the balance weights. Note, particularly, the extraordinary consistent amplitude between positions (2). We would normally expect a 20 to 40 degree difference. This consistency virtually eliminates anisochronistic effects in positions. Note also the (estimated) lift angle of 35 degrees (3).

    I suspect that the short, equal-radius locking action, equal impulse to the balance in both directions, and, most importantly, the small lift angle of the co-axial escapement contribute to the remarkable positional performance of the Omega Co-Axial. In a conventional lever escapement, a steeper locking angle is normally used on the exit pallet than on the entry pallet. This difference may interact with gravitational influences in positions (e.g. with the exit pallet down). In the conventional lever escapement, differences in impulse to the balance running in different directions may, likewise, interact with gravitational effects in vertical positions.
    (Remember at the time of Mr Odet's review, the coaxial escapements manufactured by Omega were receiving too much lubrication, which may have deteriorated their performance).

    I thought the very purpose of the Tourbillon was to eliminate anisochronistic effects in positions.

    So, my question stands: which of the Tourbillon or the Coaxial escapement is the better technology, with regards to accuracy?

    Thanks for your consideration.
    Last edited by Francois Boucher; September 25th, 2006 at 04:04.
    François – Quebec City, QC

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    Re: Omega Cal. 2500: isochronism and accuracy

    Quote Originally Posted by Francois Boucher
    I really appreciate your thoughtful answer to my initial post.

    However, I want to explore the issue of accuracy further.

    I'm not a mechanical engineer, nor a watchmaker. But I figure that if the coaxial escapement decreases friction in the system, it must also increase isochronism by incrementally reducing dynamic and positional friction, and thus, irregularities in the movement of the anchor and balance amplitude.
    I don't know if the co-axial escapement reduces friction for all positions, or only some positions, or even provides variable friction to account for dynamic irregularities caused by different positions of the watch. My understanding is that it is design to lower the frictional losses experienced in a conventional escapement mechanism, allowing lower servicing intervals and a greater power reserve. Perhaps, over a very long time, the watch will also be more accurate since there is less wear - if you assume that wear is a by-product of friction, however slight. It seems to me that the extent to which the co-axial mechanism provides greater resistance to positional variances, by nature of its design, is almost an indirect benefit - as the reviewer implies (he only "suspects").

    By comparison, the tourbillon is designed explicitly to remove positional variances, providing a mechanical solution focused purely on fixing the root cause of the problem. From reading the review quoted, the benefits wrought by the co-axial mechanism seem to be more of a happy corollary. As I said, it's possible to have a watch with both a tourbillon and a co-axial escapement, so it's not really a question of "one or the other". If you sought a relatively low-cost improvement to a conventional watch movement, one which (according to one review) also had a positive effect on positional dynamics, then the co-axial is probably a good idea even if it doesn't appear to have been designed to get at the root cause of positional imbalances.

  6. #5
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    Re: Omega Cal. 2500: precision timekeeping

    I recently bought a new-to-me one year old PO that is currently running +2 seconds total over eleven days. I like it! I have an Aqua Terra (2500C) that varies a bit, between +0.5 sec/day and +3 sec/day. It seems to change every time it runs down between windings. Currently, it seems to be running a bit faster than the +3, but I haven't been wearing it lately because I just got the PO.

    Maybe it is time for an winder....

    Phil

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