Watch Accuracy: Technical Discussion & Measurement

Moderator patrick_y shares a compelling personal anecdote that challenges common assumptions about watch accuracy and servicing. His experience, initially rooted in a belief that five days of consistent timekeeping indicated perfect health, was gently but firmly corrected by a respected watchmaker. This article delves into patrick_y's subsequent investigation, offering valuable insights into why determining a watch's true accuracy is far more complex than many collectors realize.

The Genesis

A watchmaker once told me that I needed to service my watch.  I said no, I didn’t need servicing, citing “I’ve been wearing the watch five days straight and the watch has kept perfect time.”  

Before we assume the watchmaker was greedy, let me state the watchmaker is a well respected watchmaker here on WatchProSite.  He only makes and services one brand of watch and does not service the brand of watch I happened to be wearing during the situation above.  So he definitely wasn’t mentioning it for his benefit!  

The watchmaker didn’t argue, but suggested my “five days” of evidence was “superficial.”  And for a long time, I didn’t know what he meant – wasn’t my “wear the watch five days straight” approach bulletproof?  Hmm.  One of the things my mentor taught me was, “you don’t know what you don’t know.”  Perhaps this was one of those things!  

Raw Data

Let’s look at some raw data:

Wow!  That’s a lot of raw data.  But what do these columns mean?  Columns 1, 2, and 3 are self explanatory; but columns 4 and 5 are important; 4 is the total deviation from atomic time, and 5 is the difference (amount gained or lost) since the last measurement in the row above.  We really want to pay attention to columns 4 and 5. 

Pertinent Disclaimers

The watch is a COSC Certified watch, certified to be within -4/+6 seconds a day in all positions, and was completely within the warranty period (COSC certification is not guaranteed for watches outside of the warranty period).  Obviously, a watch should be accurate every day.  

Interpreted Data

I’d like to split this data into three phases.  

Phase 1:  We can see here that the dates 05-October to 11-October, the watch behaved within COSC Specifications, never exceeding -4/+6 seconds a day.  Very good performance!  

Phase 2:  12-October to 15-October, you can see this watch is starting to behave strangely.  Gaining approximately 9 seconds on the 12^th, 19 seconds on the 13^th of October, and 23 seconds on the 14^th of October.  The watch all of a sudden became a very inaccurate watch.  Way outside of the COSC specs.  You’ll even notice I tested for magnetism on the 14^th of October, no magnetism was present.

Phase 3: 16-October to 20-October, you can see the watch is behaving normally again, very accurate.  Gaining only 7 seconds in four days!  That’s great performance.  

Ways To Misinterpret The Data

I think we can all agree, this watch is NOT accurate.  And probably wouldn’t pass COSC testing at this stage.  

But, had we only looked at a “five day” stretch in Phase 1, we’d have thought the watch was wonderful.  A great watch!  Nothing to complain about.  Always within the -4/+6 seconds as COSC testing would prescribe. 

But, we never considered had we just looked a day or two into Phase 2, we’d be stripping this watch of its certification!  On the 14^th of October, I thought the watch was magnetized, but after a compass test, nothing moved the needle.  How odd!  

And look at phase 3, the watch somehow regained all of its accuracy!  What’s going on with this watch?  

So it’s important to not just look at a small subset of data.  Watchmakers typically look at a watch for two weeks or more and at different states of wind!  When I said “five days” and an unscientific test, that was much too “superficial” for their standards!  

How Watchmakers Perceive Us Consumers

Consumers in many cultures often think, “the customer is always right.”  And to watchmakers, they would often disagree with this motto – especially when it comes to our “superficial” interpretations of accuracy.  

Watchmakers often say that customers always misunderstand accuracy.  And it's a complex topic to discuss.  And did you know accuracy and precision are two separate things?  So much to learn!  

I can now have empathy for the watchmaker in the beginning of my story...  

Conclusion

I see the error of my ways!  As a consumer, I shouldn't try to define watch accuracy on my own terms.  And my terms; the "five days of continuous wearing" I now see as woefully inadequate.  And now I realize why watchmakers take two weeks or more for their accuracy tests.  I’ll be a little more patient for my watch in the future! 

Please comment!

Has a watchmaker helped you grow your understanding of this hobby (and grow a little more as a person)?  I invite you to please tell us what happened and what you realized!