From: '''newspam'''@nonad.co.uk   
      
   On 07/01/2026 15:41, TTman wrote:   
   > Bac in the early 80s, I nade a lot of money selling 'better than normal   
   > accuracy' digital watches. A colleague designed and made an accuracy   
   > tester that showed +/- 20 seconds/month. The source accuracy was from   
   > MSF Rugby RF transmitter ( 1 pulse/second?). The detector ( I think) was   
   > some form of piezo... it was about 2mm diameter glued into a BNC housing   
   > ( for simplicity). It worked by touching the piezo probe onto the back   
   > of the watch ( with the back off) and I was able to adjust the trim cap   
   > to get close to a few seconds per month ( ignore ambient/body temp)   
      
   Watches tend to have better stability than wall clocks because for more   
   than half the time they are clamped to roughly body temperature. Some   
   kit today uses GPS when available to set its local clock.   
      
   > This probe went into the box via a cable, was amplified and somehow   
   > comaped to the source and converted into secs/month.   
   > Can anyone figure out how this probe was constructed?   
   > Reason- I want to build another one with a 10Mhz reference Xtal etc.   
   > any suggestions welcomed.   
      
   I suspect it was a high Q tank circuit or a watch crystal tuned to   
   nominal ~32768Hz to act as a passive amplifier of the stray radiation   
   from the watch oscillator. Amplify to a logic level and count number of   
   pulses over fixed time intervals from the stable reference source.   
      
   Unless you oven the crystal and calibrate it periodically you really   
   want a better reference standard. MSF Rugby or equivalent is pretty good   
   for 1 to 10000s delays so long as the dew has evaporated (after ~10am).   
      
   We used MSF as a time reference to discipline local Rb clocks for early   
   low frequency interferometry and could easily detect diurnal shifts in   
   their pulse timing due to loading of the transmitter when the ground had   
   dew on it in the mornings and late at night.   
      
   You can do it the slow way over a few days against any cheap domestic   
   atomic clock. I doubt if it is really worth the effort of making such a   
   tester today. So many smart watches use the internet or GPS for time   
   reference that they are already well synced.   
      
   --   
   Martin Brown   
      
   --- SoupGate-DOS v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)