Accuracy and Precision

[RichardHarris123]

@mikepilk, I  don't know if 50⁰ is high but the standard deviation is high, my point wasn't to show any errors in your watch but to use your data to show that precision and accuracy aren't the same thing. Your watch isn't precise but is accurate.  Many apologies, I  feel that texting lacks nuance and sometimes can be misconstrued. 

[mikepilk]

My point is that there's no point taking SD's of amplitude. The difference between amplitude horiz to vertical is a consequence of the design of the watch. It's always going to be there. But SD's of error in all positions is the right thing to do. I wrote a spreadsheet for dynamic balancing where I work them all out 

(That crown left value is bugging me though. It's a watch where I can easily get the balance out when it's cased. I might have go tomorrow shaving a touch of a balance screw).

[Nucejoe]

Hi mike, 

 This is the watch that I gathered you didn't poise after restaffing, each rate tells how close to center of circle did your watch land the dots, 

 

IN 

DD position it runs precise

DU position runs precise.

 

CL not precise.     a fautt in escapement. 

If we were to presume the fault is in the oscilator , then you can even predict where the heay spot is located.  

refer to the image of trigonometric circle.

Heavy spot is in half circle from 180 deg to 360 degs, iin other ward 3rd and 4th quarter , when the heavy spot is traveling upward against gravity.

 

 

 

 

 

 

 

 

Edited March 8 by Nucejoe

[Nucejoe]

4 hours ago, aersmwag said:

As a former competitive shooter and coach, I can really connect with the examples you've given, Joe. In the realm of watchmaking, especially when it comes to timekeeping, would accuracy be similar to seconds per day (s/d), and would precision correspond to the variations in position?

Yes  , as can be seen Mikes longines is accurate but clearly imprecise because of the rate in CL position, so you would check the gun or bow-arrow of the shooter in CL position to correct the fault. 

If Mike left his watch to run over night in CL position  , the watch would no longer show  accurate time , but on wrist  rates of all positions  avgs out  to an accurate mean rate.

Rgds

 

 

 

[mikepilk]

The different rate at crown left on my Longines was bugging me. So as golf was rained off yesterday, I decided to have another go at dynamic balancing. 

After 9 iterations I got the numbers below. I could have had one more go to get even closer, but when wearing the watch it will mostly be CL and CD, and as these are -4 and +5, they should cancel out.

And it takes time. Each iteration is taking timegrapher readings in all positions at full wind and about 160° amplitude. Remove the balance and remove some metal from the appropriate screw, put it back together and repeat. 

In my previous figures I had the hairspring pushing on one regulator pins too much. After correcting the vertical amplitudes are much better.

       Amp    +/-s
Du    296      3
DD    299    -4
Cu    275     -6
CL    283    -4
CD    284     5

And now I should be both accurate AND precise. 

(After 8 hours wear today, still within 1s of true time)

I won't be doing this with many of my watches, it's hard work! 

....... and of course there's other effects - partial winding, temperature, the watch actually moving on the wrist. Maybe I'll try swinging it on the timegrapher!

Edit: As an afterthought - I posted previously about how flat the end of the balance pivots look on these movements. This has the effect of more closely matching vertical and horizontal amplitudes, as can be seen in the figures. I read that this technique is used in some high end pocket watches. 

Edited March 11 by mikepilk

[Nucejoe]

3 hours ago, aersmwag said:

The comparison between Mike's watch and tweaking a shooter's gear really makes it click for me. It's cool how a watch's accuracy changes with its position, kind of like adjusting how you hold a bow or gun. Really appreciate the insight!

How about more insight?   

here,

Staic poisin is like aim and shoot when one is sitting on a chair,

Dynamic poising is like aim and shoot as one is riding his arse.

lol  

Edited March 11 by Nucejoe