Measuring accuracy

[ROLEXROLEXROLEXRO]

Hello, I just picked up my first Rolex, a new Milgauss! My question on determining accuracy--- the +2/-2 Spd is supposed to be an average over what time frame?

Cheers!

[thenewrick]

1 day

[ROLEXROLEXROLEXRO]

I understand it's +2/-2 seconds per day... but this advertised value is an average. My question is-- is it an average over 7 days? 14 days? 30 days? etc.

[huba01]

Oh boy , here we go again

[flytier]

The +2/-2 deviation is over eternity.

[BillA]

the -2/+2 is a 24 hr measurement. I think if you check every day you will drive yourself nuts. As they says “set it and forget it”. Check back in a week. They say it should not matter how you leave your watch when you are not wearing it but I find my watch keeps better time when face up. At night when I take the watch off before bedtime I put it in the service pouch face up on my night table. I set my watch about a week ago and recently checked it against time.gov and it was almost dead on. I was very surprised. Good luck and have fun.

[Likestheshiny]

It's an average over one day. It might be +3 for half the day, and +1 for the other half, but it will average to +2.

Although it's not so much about time as about position. Accuracy will vary positionally because of gravity. It might be outside the -2/+2 range in some positions, but as long as in the end with normal wear it ends up within -2/+2, then it's within specs.

[Jpccarguy]

You will receive a million suggestions. I have found that observing and wearing one watch over several days or a week can be helpful. You can try leaving it on 24/7, or leaving it off at night. You can leave it dial up, dial down, crown up, down, etc, to see what affects accuracy. I suspect each watch, not just Rolex, has its own personality. At least, that's true for mine. It's a great way to bond with your reference, as you learn more about it, and know it at a deeper level. Yes, you're right- I'm in love with my watches!

[EEpro]

It's the average of all positions and may or may not be achieved with your wearing habits.

[ROLEXROLEXROLEXRO]

Originally Posted by Likestheshiny

It's an average over one day. It might be +3 for half the day, and +1 for the other half, but it will average to +2.

Although it's not so much about time as about position. Accuracy will vary positionally because of gravity. It might be outside the -2/+2 range in some positions, but as long as in the end with normal wear it ends up within -2/+2, then it's within specs.

finally you understand what I'm saying.

If I just measure 24 hr and it's +5, it doesn't mean it's out of spec because tomorrow it may be +1, and the next day -1, etc. the average over the days will be +1.7 which is within spec. This is getting into accuracy vs precision. Analogy is if I throw 5 darts at a bullseye and I completely miss the bullseye every time, I have poor accuracy but if all 5 darts landed in a tight group, I still have precision...

Anyway. I don't think Rolex indicates what +2/-2 seconds per day is referring to in terms of average range.

[Arid]

I believe there’s a medical term for that!

[chinaski]

FWIW my Tudor BB Steel (In House) is running -6 after 4 days. My 14270 Explorer keeps equally exceptional time.

I set my watches to Time.Gov

[Sebastian5]

I use watchtracker app occasionally, I set it when the seasonal time changes and add a datapoint every 1-2 month or so.

Long term measurements vary from -0.1 to -0.3 on a 2,5 year old OP39. Pretty impressive and way better then the -2/2

[Andad]

Originally Posted by ROLEXROLEXROLEXRO

Hello, I just picked up my first Rolex, a new Milgauss! My question on determining accuracy--- the +2/-2 Spd is supposed to be an average over what time frame?

Cheers!

Wear it in your normal pattern for a few weeks to satisfy those who think a settling in period is required.

Set it to the correct time.

Wear it in your normal pattern for a few more weeks.

Divide the gain or loss by the number of days.

That will give you YOUR result.

Let us know the result?

Once you have the average for your pattern there may be a +/- positional correction you can use if you want to go that far.

[bmb15]

Originally Posted by Arid

I believe there’s a medical term for that!

Exactly! I suggest the OP compares with the rates (s/d) measured underwater at -300 m, -200 m, -100 m, in a swimming pool and corrects these new data for the different water salt content. Exact time setting must be done underwater.

Btw, Rolex movement specs are as follows
PRECISION
-2/+2 sec/day, after casing !!!!
Otherwise COSC [-4,+6]

[Andad]

Originally Posted by bmb15

Exactly! I suggest the OP compares with the rates (s/d) measured underwater at -300 m, -200 m, -100 m, in a swimming pool and corrects these new data for the different water salt content

Btw, Rolex movement specs are as follows
PRECISION
-2/+2 sec/day, after casing !!!!
Otherwise COSC [-4,+6]

Very clever.

But incorrect.

[bmb15]

Originally Posted by Andad

Very clever.

But incorrect.

Facts



Rolex guarantees your watch is accurate to -2/+2 seconds per day, after casing. Comparable with the -4/+6 seconds per day for the uncased movement that COSC requires.

[iTreelex]

Rolex needs to step up their game to +0.5/-0.5 per year come on now

[Andad]

Rolex guarantees your watch is accurate to -2/+2 seconds per day, after casing. Comparable with the -4/+6 seconds per day for the uncased movement that COSC requires.

You are stating that Rolex guarantees your watch is accurate to -2/+2 seconds per day.

But your cut and paste from Rolex.com it states a guaranteed precision of -2/+2 seconds per day.

Precision and accuracy are not the same thing.

The OP’s question was about accuracy and only a wearing pattern will give him this information because he will not reproduce COSC test positions or Rolex’s own final positional adjustments and retesting.

[bmb15]

Buddy, you seem to be a smart fellow too ... Trust me, I know the difference between accuracy and precision! Therefore, of course it should read "Rolex guarantees your watch is precise to -2/+2 seconds per day, after casing."

[MrJKLFoams]

Wear it enjoy it because one is not enough. Congratulazione by the way...now start building your colleczione!

Sent from my SM-G988B using Tapatalk

[Andad]

Originally Posted by bmb15

Buddy, you seem to be a smart fellow too ... Trust me, I know the difference between accuracy and precision! Therefore, of course it should read "Rolex guarantees your watch is precise to -2/+2 seconds per day, after casing."

What you mean ‘seem to be’.

[padi56]

Originally Posted by Arid

I believe there’s a medical term for that!

Yes it's called {CCTS} constant checking time syndrome.

[bmb15]

Originally Posted by Andad

What you mean ‘seem to be’.

Buddy, not sure if you are a smart fellow or a know-it-all fellow. With 31880 posts probably the latter one, only joking! More important, let's wait for the OP's report about his upcoming underwater timegrapher measurements.

[bmb15]

Originally Posted by padi56

Yes it's called {CCTS} constant checking time syndrome.

Great, I learned something in this exciting thread.

[Dazlewis]

Originally Posted by ROLEXROLEXROLEXRO

finally you understand what I'm saying.

If I just measure 24 hr and it's +5, it doesn't mean it's out of spec because tomorrow it may be +1, and the next day -1, etc. the average over the days will be +1.7 which is within spec. This is getting into accuracy vs precision. Analogy is if I throw 5 darts at a bullseye and I completely miss the bullseye every time, I have poor accuracy but if all 5 darts landed in a tight group, I still have precision...

Anyway. I don't think Rolex indicates what +2/-2 seconds per day is referring to in terms of average range.

Your question suggests you have not grasped the concept. The claim is that when if you set you watch on one day, it I’ll be correct to within 2 seconds at the same time on the next day. That’s all there is to it. It is not telling you anything about how the time varies in the day, although one would naturally expect the deviation across 24 hours to accumulate smoothly across the day - i.e. it won’t run perfectly for 23 hours and 59 minutes and then suddenly lose or gain 2 seconds over the last minute.

It also doesn’t tell you what will happen over multiple days. If the error is systematic, then if it is out 2 seconds after one day, it will be out 4 seconds after 2 days, 6 seconds after 3 days, and so in. If the daily error is randomly distributed about a mean of exactly 24hours, it will regress to perfection with increasing number of days - the error over n days being the error over one day divided by the square root of n. It is of course most likely the error will be almost entirely systematic!

[Greg 59]

Originally Posted by ROLEXROLEXROLEXRO

Hello, I just picked up my first Rolex, a new Milgauss! My question on determining accuracy--- the +2/-2 Spd is supposed to be an average over what time frame?

Cheers!

I'm afraid that you are just going to have to accept the fact that Rolex watches are not that accurate but the majority of owners don't like to admit it so they will try to ridicule you into thinking that it's petty to want your very expensive trinket to do what it says it will do.

I have a bunch of Rolex watches and none of them will tell the time as well as my three Omega calibers regardless as to whether I wear them 24/7, place them crown up, face up, face down, or even ensure they are fully wound by manual winding every 8 hours.

The tem "chronometer" leaves a lot to be desired, probably dreamt up by the Swiss watch industry to bolster their own financial interest. Many Swiss watch companies don't even bother with COHS these days because it is pretty mediocre and not worth the extra cost involved.

[Andad]

Originally Posted by bmb15

Buddy, not sure if you are a smart fellow or a know-it-all fellow. With 31880 posts probably the latter one, only joking! More important, let's wait for the OP's report about his upcoming underwater timegrapher measurements.

Why doesn’t Rolex state that their new movements have an accuracy of +/- 2 seconds per day.
Why do they state precision?
They obviously also know the difference.

Is it because the movements could be running 5, 10 or even 8 seconds per day fast or slow consistently (with precision) at +/- 2 seconds per day?

I believe the new movements may run at +/- 2 precision and can also be adjusted for accuracy but I know not many of them do long term.

[bmb15]

Originally Posted by Andad

Why doesn’t Rolex state that their new movements have an accuracy of +/- 2 seconds per day.
Why do they state precision?
They obviously also know the difference.

Is it because the movements could be running 5, 10 or even 8 seconds per day fast or slow consistently (with precision) at +/- 2 seconds per day?

I believe the new movements may run at +/- 2 precision and can also be adjusted for accuracy but I know not many of them do long term.

The following definitions plus the sketch hopefully clarify the used terms.

Accuracy is how close a measured value is to the actual (true) value.

Precision is how close the measured values are to each other.



An example:

(1) You correctly set the time of your movement at t = 0 using a well-known reference, e.g. an atomic watch.
(2) After 24 hours, you measure a deviation of +15 s compared to your reference source.
(3) This measurement (after 24 hours) you repeat (for example) 100 times and your results vary between +13 s and + 17 s.
(4) Then your movement has an accuracy of +15 s/d and the precision is +/- 2 s/d

That is my understanding of the used terms "accuracy" and "precision".

[EEpro]

Originally Posted by bmb15

The following definitions plus the sketch hopefully clarify the used terms.

Accuracy is how close a measured value is to the actual (true) value.

Precision is how close the measured values are to each other.

Here here, you're speaking my language. I design clocks for a living. But not these types.