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Discussion Starter #1
Hi... I am new around here, joined just two months back, after purchasing a new AT master coaxial, blue dial. I like the watch. I have been checking its time compliance off and on, I have made the following observations. (note I am not talking about accuracy, I have read and understood that that term has other meanings).

When new, about 10 days on the wrist, I measured the daily rate at +0.4 seconds or so (averaged after 5 days). The next 5 days indicated 0.55 seconds, I left it to my measurement inaccuracies. Checked the watch again after about 50 days, watch is running faster... about 1.8 seconds/day. Checked twice over two 5-day periods, no significant difference. Settling in time? (I used "WatchCheck" App on Android for all measurements)

Immediately after the last check I wanted to evaluate the power reserve... and I got the following prompting me to raise this question. Watch was kept dial up, around 30 degree C (Saudi Arabia!!). The first 12 hours gave the daily rate of +1.9 seconds. The next 24 hours gave 4.2 seconds. The next 12 hours gave 5.1 seconds/day. The last 12 hours gave 5.3 seconds/day. I have now wound the watch (did not allow it to stop), and am wearing it.

I will check the daily rate again on 5 day average from now, will be available only after 5 days...

Now, my question is - Does a watch run faster as it winds down from full power to zero power? I am not worried (yet), but some comments would be very much appreciated.

Thanks!!
 

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My Omega PO runs slower as it winds down, so does my DSSD.
 

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My understanding is that many, but not all, watches run faster as the amplitude decreases.this has been compared to the way a swing has faster oscillations as its arc decreases.

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Discussion Starter #4
Thanks guys... encouraging replies, both. I guess I have one that runs faster. Will continue tracking, anyway.
Pretty decent watch the AT master Co... difficult not to fall in love with it. I am sure I will not be let down!
In the meantime hope to see more comments.
 

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My understanding is that many, but not all, watches run faster as the amplitude decreases.this has been compared to the way a swing has faster oscillations as its arc decreases.

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^^^^ This.

Think of it as gas mileage it varies due to so many widget that most people don't even think about.


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I've never owned a watch runs faster as it unwinds, always slower. Seiko 7s26/4r36 can lose 30 sec. overnight, a few recent SW200s were just as bad. The effect is called isochronism which oddly is not checked by COSC for chronometer certificates.
 

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I've never owned a watch runs faster as it unwinds, always slower. Seiko 7s26/4r36 can lose 30 sec. overnight, a few recent SW200s were just as bad. The effect is called isochronism which oddly is not checked by COSC for chronometer certificates.
Yes, it is. Read the full COSC specs.

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Here's my understanding on this subject.

As the mainspring unwinds, it produces less and less torque to drive the movement. Now as we know, it is this torque that decides the amplitude of swing from the balance wheel. That is to say, when the escapement provides an impulse to the balance wheel to maintain its swing, that impulse slowly becomes less and less forceful as the mainspring unwinds.

What happens then is that the balance wheel will not rotate the full 270-300 degrees that you would expect in (most) fully wound, well-maintained movements. Instead, the arc becomes shorter and shorter. As this arc becomes shorter, it would theoretically take less time to complete the swing, and this results in the noticeably faster rate.

That's the theory, of course. But there are many other factors along the way that will decide exactly what happens as the watch winds down, so it's not a law so much as it is a guideline in terms of how a watch performs at lower winds. As others above have mentioned, there are indeed watches that run slower as it winds down, or stays the same. That's when you know that other things have come into play.

Watch mechanisms are truly beautifully elegant, almost Rube Goldberg-esque little machines, that it's tough to point at any one thing and deem it to be the deciding factor. So many small components playing so many different roles, in addition to minor variations in tolerance, often add up to an idiosyncratic performance, even among watches from the same caliber.

Hope that helped :)
 

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Discussion Starter #9
Hey... I seem to have hit many threads on isochronism.. One relevant post is copied below

<<<<<<<<<<<<A perfect balance will oscillate at the same rate regardless of the amplitude of the oscillation. The balance is MORE perfect if the balance is going at high amplitude. This is partially because the friction is less. So if it is running about a turn and a half at full wind (270 degrees) and it is running no less than say 1 1/8 turn after 24 hours (202 degrees), then you are on your way to isochronism.

The shape of the hairspring at both ends is also very important. This is called terminal curves. The breguet overcoil was a very important creation for improving isochronism, but good isochronism can also be achieved with a flat hairspring if the terminal curves are correct. The shape is critical for both. For example, if the overcoil approaches the staff too closely, the watch will be go faster as the mainspring runs down (short arc). If the overcoil is too far from the staff, then the watch will slow down as the mainspring runs down.

The amplitude of the balance also effects positional errors. If the balance is out of poise or the hairspring is out of round you will have a positional error in specific pendant positions at a full wind. When the action drops to about 1 1/4 turn, the positional dissappears. As the action drops below 1 1/4 turn, the position error returns, but in the opposite direction. Postional error is also larger in the smaller arc. So we want the watch to spend more time above 1 1/4 turns and below 1 1/4 turns. Then if we have positional errors, they have a greater chance of cancelling out. The watch will run slightly fast for while, then slightly slow for a while and be back on time at the end of the day. Of course, we hope we have most of the positional error adjusted out.

The spacing of the regulator pins also affect isochronism. If the regulator pins are too far apart, then the hairspring vibrates from regulator pin to the other regulator pin at high arc. However, at low arc, the hairspring will not touch one or both of the pins, which effectively lengthened the hairspring and slows the watch. We want the regulator pins as tight as possible without binding the hairspring.

I am sure I have forgotten a couple of other factors that effect isochronism, but this should hold you for a while.

Don Dahlberg
NAWCC volunteer
>>>>>>>>>>
 

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Great post but I think there's a few typos in his third paragraph. I think he meant that above 2.25, the movement was inaccurate, from 1.25 to 2.25, the movement was most accurate, and below 1.25, the inaccuracies returned. Of course, I'll be easily convinced that I'm wrong.

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Discussion Starter #11 (Edited)
After having read much on Isochronism on this forum and also other places, this is what I think...

In my particular case, considering 60 hours power reserve as 100%, my time compliance seems to have held for at least 12 hours... say 80%. The lack of isochronism seams to have manifested during the next 24 hours, possibly around 65%... and then onwards increasing steadily towards he 0% point.

I also understand that the principal method for control of isochronism is the design (and compliance to specs in its manufacture) of the mainsprings. The variabilities in the making process can therefore influence its performance?

Also, as the springs age its properties can change... ever so slightly and so ?

Open questions these, If anyone would like to comment.

Incidentally, my watch is no back at 1.8 sec day... good!
 

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I've always wondered about this, I have two watches that will run fast as they power down. I first noticed this on my Christopher Ward SH21 5 day, fully wound it will run dead on at +.2 to +.4 sec per day for the first 24 hours after that it will start to run faster. I also have a Seiko with 6r15 (50 hour) that also does the same thing, I've noticed the amplitude on the Seiko drops rather quickly though.
 

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Discussion Starter #13 (Edited)
Guys... I have made more observations last two weeks, and I am confused - to say the least.

The second power down test again lasted 60 hours, kept the watch 12 up. Watch was running 1.7 s/d worn. Increased to 2.4 s/d first 24 hrs. dropped to 1.6 s/d the next 24. Last 12 hrs at 0.2 s/d!!!
Wore it then without winding and got 4 s/d over 24 hrs. Rate dropped to 3.3 s/d the next day. Manually wound to full power and it is still at 3.2 s/d.
Either something is wrong with my watch, or the rates vary all over within COSC standards, don't know what.
I think I will give up my testing!!!
 

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Isochronism is a large factor in watch accuracy. I have one watch, an SW200, that loses time like crazy it's last 6 hours of power reserve, -30 seconds. Might as well subtract 6 hours from the 38 power reserve when it comes to accuracy.

I read that COSC does not test for isochronism. Watches are tested at 30% wind, which assumes a sedentary lifestyle.
 

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I have the AT >15000 gauss with the 8508 movement (which I believe it is the same as the 8500 but it was the first with the new master coaxial and has different numbers engraved). I believe mine gets slower as the power reserve winds down. Also wait a while for the time to settle down. After I got mine back from service, it was +0.5 spd, then went to +1.0 spd over a month's time, and then +1.5 spd after 3-4 months. Around 6-8 month mark it has been +0.5 spd and stayed there for the following 6 months (today). I have the watchtracker app and put in a data point every now and then so I have all this data on hand.
 

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Isochronism is a large factor in watch accuracy. I have one watch, an SW200, that loses time like crazy it's last 6 hours of power reserve, -30 seconds. Might as well subtract 6 hours from the 38 power reserve when it comes to accuracy.

I read that COSC does not test for isochronism. Watches are tested at 30% wind, which assumes a sedentary lifestyle.
COSC tests at 100% power reserve to the best of my knowledge.

Omega's new METAS whatever apparently tests accuracy difference between 100% and like 30% or so. Nice test, just wish it was a bit easier to afford those watches.


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Discussion Starter #17
To m0c021
One question... why did you have to service your AT>15000, question because it should not have completed even 4 years?

My watch seems to be running all over, no consistency? I am a bit worried about that... After the first power down test, I wound it full and it recovered to +1.8 from the last +7 or so, immediately. On the second test, 12 up, the behaviour was different, it ended the trial with +0.2 s/d. I did not wind it up this time, and during the next 24 hrs or so of run it was 4 s/d. The next 24 hrs gave me 3.4 s/d, then I wound it up full, and got 3.2 s/d. Possibly it is improving now, cant be sure, looks like 2.2 s/d right now... A lot of inconsistencies.

After every major change in the spring tension status it appears to need stabilisation time? Doesn't make sense.
 

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Were both tests 12-up? If not, then you are comparing apples to oranges. Likewise, comparing 12-up to wearing the watch is apples to bananas. I suspect if you run two tests with identical conditions each time (same orientation, fully wound by hand before starting), you will get nearly identical results.
 

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Discussion Starter #19
Were both tests 12-up? If not, then you are comparing apples to oranges. Likewise, comparing 12-up to wearing the watch is apples to bananas. I suspect if you run two tests with identical conditions each time (same orientation, fully wound by hand before starting), you will get nearly identical results.
If you read my original post, the first test was dial up. So I understand the difference in the results between dial up and 12 up. What I don't understand is why after winding them full, while wearing, it was 1.8 s/d first time, and then 3.2 s/d the second time (though I delayed the winding up by 48 hours)... but seem to be recovering now slowly after a further 36 hours after winding up (hopefully).

Does a watch require a few days time to stabilize at any pattern of use after a power down test?
 

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To m0c021
One question... why did you have to service your AT>15000, question because it should not have completed even 4 years?

My watch seems to be running all over, no consistency? I am a bit worried about that... After the first power down test, I wound it full and it recovered to +1.8 from the last +7 or so, immediately. On the second test, 12 up, the behaviour was different, it ended the trial with +0.2 s/d. I did not wind it up this time, and during the next 24 hrs or so of run it was 4 s/d. The next 24 hrs gave me 3.4 s/d, then I wound it up full, and got 3.2 s/d. Possibly it is improving now, cant be sure, looks like 2.2 s/d right now... A lot of inconsistencies.

After every major change in the spring tension status it appears to need stabilisation time? Doesn't make sense.
My watch was running perfectly at +0.5 spd for a year and then was running at +10 spd. Had it serviced under warranty and they fixed it for free even though it was due to extreme shock which is not covered under warranty. Only shock that it would have experienced was me firing maybe a hundred rounds of 9mm with the watch on my off hand wrist. So I take my quartz to the range now even if my watch is suppose to be able to handle it, just in case.
 
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