I was lurking around this forum early this year when I was looking for information about my Seiko Black Knight which has a 7S26B caliber.
I just wanted to contribute back to you guys my experience in regulating this watch.
After reading in here I decided to try regulating as the Seiko was +7s fast. I'm a stickler for accuracy but bought the Black Knight auto because it looked so cool, was cheap and best of all was a true diver's watch. I really like its look till even now.
Anyway I wasn't happy about the accuracy and wanted more so decided to try regulating. I downloaded an excellent pictorial how-to from somebody I can't remember now and bought the tools from some watch tool website and after arriving, started to try.
First few tries were bad and made accuracy worst. After many more practices I got better and finally managed to actually get it down to something like +/- 1s per day! It stayed at this accuracy for a couple of weeks then started to stray and then reached +7s per day again.
Once again I went through the process of regulating and got it to +2s per day and once again after some time accuracy starts to stray.
My watch wearing routine doesn't change much and I figure that the 7S26 doesn't really like being tighter than +/- 7s per day. I think its the nature of this mechanism and 7s or thereabouts is the baseline of this particular caliber.
However, I discovered that when I don't wear the watch when I sleep at night, it actually increases by +3s per day. So what I did was I regulated it so that it stabilised at -7s per day and then I alternate between wearing it for two nights and then NOT wearing for one night and so far the watch seems to vacillate between +/-5s and I have not needed to adjust my watch for months now! It still keeps within this tolerance to the atomic clock time.
That's the lesson here:
1) The 7S26 doesn't hold accuracy better than 7s for long periods. It will find its way back to this
2) Make use of the overnight speeding up of the watch and regulate so that it's slow when worn during day and the two will balance each other so that the daily variation is almost zero!
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