Ebay Watches Accuracy
- February 22nd, 2012
- Posted in Hacks & Mods . Unclassified
- By BadWolf
- Write comment
-Inexpensive
-Good looking
-Kinda reliable
-Really nice mechanical interior,fun to watch and show
Ok so now,everybody know that often,cheap good looking stuff can’t be reliable.
So upon receiving 3 of em, I wondered just how accurate they were at keeping time….
First obvious point : why don’t you set them and just check the next day? It’s pretty simple,they are mechanical watches,if you don’t wear them,they won’t crank back up and stop pretty quickly. If you wear them 12h/day,they will last forever.
So, a device of some kind was needed to check the Accuracy…
Unfortunately, I’m not at home,where I would have used an arduino to do data acquisition and count up the “ticks” on a definite time length.
Then I got an idea : my pentax WG-1 GPS has a pretty cool intervalometer built-in that can take pictures every minutes for a long period…why not use it to gather “stroboscopic” images of the watches running, if they are accurate,the seconds counting hand should stay still while the minutes and the hours go on.
Second Obvious point : What tells me that the camera is accurate?
Solution was to make a first “video” at 1min intervals of a Real time clock,the only one I could find near me was an online website : http://atomicclock.org/
Here’s the video of the snapshot taken of the clock :
As you can see,it’s pretty darn accurate,somewhere about 0,2 s.
From that point,I was ready to go on and test those :
Here is the resulting video:
Analysis base on a timescale of 2hours and neglecting the camera’s error:
Watch #1 :
Lost 2 seconds
-2/7200 = -277.778E-6 seconds
Error of -0.02777 %
Error for one day : -24 sec
Conclusion: Pretty accurate.
Watch #2 :
Gained 14 seconds
14/7200 = 1.944E-3
Error of 0.19444%
Error for one day : 2 min and 48 sec
Conclusion : Not accurate enough
Watch #3:
-2/7200 = -277.778E-6 seconds
Error of -0.02777 %
Error for one day : -24 sec
Conclusion: Pretty accurate.
General conclusion:
It is clear that W1 and W3 bears the same clockworks thus have the same error minus the variations in springs.
So this is how you find out about watches guys. Don’t get scammed,I’m returning W2 to the supplier. I have to time to waste. ;)
Cool! Could you an accuracy test on the G-Shock GA-100?
Sadly I can’t as I don’t own that particular model,but if you do,find a camera with the timelapse function and you should get pretty good results!
Do you have links to ebay where to buy these watches?
http://www.cafr.ebay.ca/sch/i.html?_nkw=skeleton+watch&_sacat=0&_sop=15&_odkw=mechanical+wrist+watch&_osacat=0&_trksid=p3286.c0.m270.l1313
Search for mechanical wrist watch and skeleton watch.
Enjoy
might have been informative to film the watch test with the website in the background, to be able to compare the accuracy.
I don’t quite see why it’s different from 2 videos… well,next time!
As-tu essayé une montre “kinetic” ? c’est-à-dire celle qui se crinque toute seule seulement en la portant.
Yup,elles en sont justement =P
That’s a really clever and inventive method of testing the watches using stuff at hand. Don’t interpret the following wrong, because I’m actually a bit impressed.
However, the test is flawed because it does not control for the position of the watches. You have watch #1 with the crown down while #2 and #3 are crown up.
The rate of a mechanical watch is influenced by many factors, and position is one of the most important, because gravity affects the mechanism differently when it is in different positions.
There’s another potential flaw in the fact that you extrapolate the 24-hour error from a short sample, but the watches’ rate is influenced by the amount of power in the mainspring (this is called “isochronism”). So the rate error you measure for the first two hours will likely not be repeated later.
To get a full picture of the performance of the watches they must be compared in multiple positions. For these cheap watches, however, it’s probably not worth testing them thoroughly, because they are what’s called “unadjusted”—only the bare minimum of effort was made to ensure that they run consistently. (High end mechanical watches, on the other hand, will have a skilled person adjust them by hand to run consistently at 5 or 6 positions, heat, cold and isochronism.)
thanks for the heads up,really constructive comment there!
I actually didn’t know much about mechanical watches before doing this so I’ll keep what you said in mind next time i’m on something similar.
By the way,are you some watchmaker or just a very clever hacker?