EDIT: All, please read the post carefully. I am not asking if my watch is within COSC or Omega's standard range

Hi all, I purchased a used PO8500 a few months ago and recently got it back from the service center due to the lume on the dial and hands wearing prematurely. This was done under warranty. It came back with the white quality control card indicating that time keeping was +0.8 seconds per day. Great.

Last week I started monitoring the accuracy. I stopped the seconds hand at the middle of the 12 o'clock marker and kept the minute hand set to the next minute. As soon as the upcoming minute started, I pushed the crown in. This was done on a full wind too. For the first 48 hours accuracy was spot on when I would eyeball it. The seconds hand passed the middle of the 12 marker as soon as the next minute started.

Here's where I'm at a loss. As of today (7.5 days later) it is -3 seconds (when the new minute turns on my phone, the seconds hand is on the 57 second mark on the watch). However, a minute later it's -4 seconds (when the new minute turns on the 56 second mark) and sometimes it's -2 seconds (when the new minute turns on the 58 second mark). I'm hoping this makes sense.

I can check the accuracy for every minute consecutively and each time it'll be a little different...-3 seconds and the next minute it'll be -2 and then the next minute it can go to -4. What's causing this? I'd like to reiterate that for the first 2 days or 48 hours it was spot on with no variation. I thought maybe the power reserve was depleting but I've been wearing the watch nonstop since last Wednesday in the morning.
Really appreciate any feedback.

 

COSC spec below:

COSC standards
all units in seconds unless specified
Mechanical
Average daily rate: −4/+6



It might be -3 seconds on day then +2 seconds next day? Or is it always losing time?
My 47 year old Speedy has lost 57 seconds over the course of 21 days.
You need to check it out over a longer test run.

Check it out in more detail here: https://en.m.wikipedia.org/wiki/COSC

I hope this helps?

 

Not quite....this has nothing to do with COSC as I know the watch was well with COSC for the first 48 hours.

As I mentioned the first few days it was spot on. I sort of stopped monitoring it after then until two days ago. 2 days ago it was still in the -2 to -3 second range. But today it was all over the place... -2, -3, -4 and then it can even go back to -2 the next minute. All within a 10 minute span.

 

My PO with caliber 8500 runs consistently at +3 seconds per 24hr period.

It sounds like the tension in the mainspring that is causing your sporadic gain/loss that you're experiencing.

 

Wring hands. I can understand your anxiety. My 30 year old Rolex DateJust is 30 seconds fast in close to three months, but hasn't varied for the past two weeks. I couldn't tolerate 2 to 3 seconds per day from such a heavily touted watch.

 

I think OP is saying that the watch is currently about 3 seconds behind true time but can gain or lose time from that point with some frequency. So from baseline of -3 seconds he's gaining/losing a second per minute every now and then. Is that right?

 

Yes this is basically what I'm trying to say. The first time I checked after a few days it was -2 seconds. I thought that couldn't be right so I checked again the following minute and it was -3. Curious again, I kept on checking every minute and it would vary from -2 to -4 seconds.

The first 2 days it was spot on with 0 deviation.

 

It's likely the phone, not the watch...try another time source.

 

I'm assuming that you get what I'm trying to explain. -3 seconds after 7.5 days doesn't worry me as it means that the watch is running well within COSC. However, when one minute it's -2 and the next minute it's -3 and the next minute it's back to -2, that's what concerns me. I'll take your suggestion and not use the cell phone anymore. Is it possible for accuracy to be this sporadic as I describe?

I reset everything and now synched the watch to the NIST time sound on time.gov. Let's see how it holds up. But I thought cell phones are supposed to be accurate with this stuff.

To reiterate, for the first 48 hours last time I reset the time on my watch, it was spot on, no deviation. And when Omega sent the watch back to me, the card they sent back with it stated that it was running an average of +0.8/sec. So those two factors make me more at ease

 

Do the math and tell me if you think it's likely, in particular given that the watch is keeping very good time over 24 hour periods...

 

Not all 24 hour periods though, just first 48 hours after I set the time and checked for accuracy it was spot on. But the last 24 hour period it's been inconsistent - one minute it's -2, the following minute it's -3, the minute after that -4 and it can go back to -2 the next minute. I suppose checking against NIST time will provide the real definitive answer though, so I'll monitor that 1x/day for a week.

 

What daily rate gain would there have to be to show a 1 second gain over 60 seconds? Do the math and tell me if you think this is plausible...

 

Update:

Last Wednesday at 7:15am I used time.gov and synched my watch with it. For the first 2 days (again), it was spot on, but after that it started losing time. This is exactly what happened last time I did the time test. As of time morning at 7:15am (6 days after), it's lost 1.5seconds. So when the new minute turns on time.gov, the seconds hand is just between the 0:58 and 0:59 seconds mark on my watch.

1.5 seconds in 6 days might be within spec, but why, for the 3rd time, does this watch only start to lose time 2 days after I start timing it on a full wind? I'd rather gain time than lose.

Would a service be in order?

 

So we have gone from you claiming the watch loses a second within a minute, to now losing just 1.5 seconds over 6 days - this is -0.25 seconds per day average - there is absolutely nothing wrong with your watch, and it doesn't need a service. If you are expecting perfection, even a quartz watch won't live up to your standards.

Cheers, Al

 

Even my Rolex Date-Just isn't perfect. It has gained one second since early February!

 

Al, I appreciate your reply, but you're missing the question at hand here. I also never said it was losing 1 second continually every minute. What I did say was it'll lose 1 second then gain that second back he following minute and maybe the next minute it'll lose that second again. I was using my cell phone to track the accuracy which you indicted might be the cause for this, so I switched to time.gov.

My question still stands. What makes the watch operate spot-on for the 1st 48 hours, then tapper off in the subsequent days? I wore it no differently during the 1st 48hours and the watch rests in the same position over night. Could it be related to power reserve?

 

That's pretty close to perfect!

 

scrap that inaccurate sucker!

Seriously... we're talking one or two seconds a day, how accurate do we need, its not like we plotting the trajectory of a spacecraft here!

 

Take it to any local watchmaker who has a good timing machine and ask them to check it out. This will show clearly and precisely If it really is massively advancing and retarding over a short one minute cycle. If it does, it sounds like a problem.

On the other hand, if a timing machine test gives it a good clean bill of health, it could indicate a problem with your time reference data or your technique, or possibly (?) an issue with the second hand mechanism itself ? (not a watchmaker - don't know if this is even a possibility).

 

If your talking of a loss/gain of several minutes a day, I can understand the frustration. My snoopy was doing this lately and thus, it is being checked out as we speak. A few seconds up/down every few days would not bother me one bit. Yes, luxury time pieces are expensive, but I don't expect them to run without variences. They are machines and it does happen. I have stopped worrying about every last second up and down, which led me to have a great and much enjoyable wearing experience.