Accuracy at various stages of wind? Ananta case study
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  1. #1
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    Accuracy at various stages of wind? Ananta case study

    I've been monitoring my Ananta closely for accuracy, as I do all my watches. I check every new watch against time.gov at least twice a day, often times as many as 4 times per day, and note the accuracy, including resting positions, daily activities and so on, when anomalies merit such notes.

    Now, my Ananta is usually incredible accurate, presuming ideal conditions: i.e., if it's worn for a normal daily period and sleeps dial up/down, it will hit about +0.5/day. It fairs much worse crown up, losing about 3 seconds overnight, assuming it's roughly fully wound before sleep.

    Now, I've noticed that as the mainspring unwinds to about 66%, it begins to slow down. It'll lose a couple seconds even in dial up position, eventually getting as bad as losing about 4 seconds a day assuming it never gets wound up past half way. (Obviously, this is a fairly contrived setup, as most people wearing their watch would have it wound quite high by day's end, but hey, this is science)

    Well, I wear it so often that I don't let it wind down to the last 25% or so, but I did this time. It was about -6 about 24 hours ago, but was at about +/-0 when I checked it recently. So it had gained about 6 seconds in a day's time, crown up, near the end of its power reserve. I didn't want it to die, so I wound it half way after measuring.

    So what are the results? Fully wound, it runs ever so slightly fast. Half wound it runs a little slow, but not badly. Nearly unwound it runs somewhat fast.

    Quite a strange result and counter intuitive. Watch movement experts, why is this so?

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  2. #2
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    Re: Accuracy at various stages of wind? Ananta case study

    That is the phenomenon known as “isochronism.”

    The reason the rate speed up as the power reserve drops is because the energy delivered to the balance drops as the mainspring nears exhaustion. The less energy delivered, the amplitude of the balance (how far to the left and right it swings) drops. As the amplitude is less the length of time required to make the swings drops, thus the movement begins to gain time.
    familiaritas parit contemptum; raritate admiratione wins.- Lucius Apuleius
    est necessry, accurate ad secundo? - Lysander magna
    iustum est horologium - Obscurus Genius

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    Member CitizenM's Avatar
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    Re: Accuracy at various stages of wind? Ananta case study

    I get the basics of isochronism, but why does the watch behave slow at half wind and fast at full wind?

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    Member lysanderxiii's Avatar
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    Re: Accuracy at various stages of wind? Ananta case study

    Quote Originally Posted by CitizenM View Post
    I get the basics of isochronism, but why does the watch behave slow at half wind and fast at full wind?
    The power output of the main spring is not flat. They try to manufacture then so they are as close to flat as possible but it will always be approximate.

    Looks to be that the designers in this case tried to get the second half of the power reserve (the half that normally would not be used much if worn for 16 hours, placed on a table for 8 and worn again for 16 hours, with a 42-ish PR) to average constant.
    Last edited by lysanderxiii; November 28th, 2011 at 19:16.
    familiaritas parit contemptum; raritate admiratione wins.- Lucius Apuleius
    est necessry, accurate ad secundo? - Lysander magna
    iustum est horologium - Obscurus Genius

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    Re: Accuracy at various stages of wind? Ananta case study

    Quote Originally Posted by lysanderxiii View Post
    The power output of the main spring is not flat. They try to manufacture then so they are as close to flat as possible but it will always be approximate.

    Looks to be that the designers in this case tried to get the second half of the power reserve (the half that normally would not be used much if worn for 16 hours, placed on a table for 8 and worn again for 16 hours, with a 42-ish PR) to average constant.
    Fascinating. I wish it was as accurate as my Orient. Now there's a champ.

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    v76
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    Re: Accuracy at various stages of wind? Ananta case study

    Orient quartz?

    I remember that my first El Primero was ridiculously accurate. I wore it continuously for about two months, and it had lost 2 seconds in 2 months! It was as though the watchmaker had regulated it to my wearing pattern.

    Usually lost a second about every 16 hours on my wrist, and gained one second every 8 hours when rested dial up (approximate gain and loss figures between 25% and full wind).

    Quote Originally Posted by CitizenM View Post
    Fascinating. I wish it was as accurate as my Orient. Now there's a champ.
    Last edited by v76; November 29th, 2011 at 03:18.
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    Re: Accuracy at various stages of wind? Ananta case study

    Quote Originally Posted by v76 View Post
    Orient quartz?

    I remember that my first El Primero was ridiculously accurate. I wore it continuously for about two months, and it had lost 2 seconds in 2 months! It was as though the watchmaker had regulated it to my wearing pattern.

    Usually lost a second about every 16 hours on my wrist, and gained one second every 8 hours when rested dial up (approximate gain and loss figures between 25% and full wind).
    Orient Automatic. I didn't let it die for the entire first year and I think it came out at +13 or something. It has died since then (dead now actually), so it screwed up the record, but it's insanely accurate. My quartzes are way less accurate, except for oddly the cheap Fossil chronograph.

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    Re: Accuracy at various stages of wind? Ananta case study

    Interesting thread and great answers. Cheers.
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