First computer with real-time clock?

[David V. Corbin]

Paul,

The system I was working on was rack-mount...on a submarine [NATO Walrus
Class - launched circa 1984]

I completely agree that there were other more accurate sources [of which
youy name a few. I should have been more precise in my statement.
I was comparing it to other board mountable electronic clock sources [since
we were discussing crystals].

The system in question actually connected to a highly accurate 1PPS External
source that was slaved to a radio clock under normal circumstances. However
our rack need to maintain time even in the event of external failures. It
was deemed that a <50mS error per day under error conditions was acceptable.


David

>>>>> 
>>>>> I was involved in the development of soms Military 
>>>>> systems  [1979-1983] that used a tempe0rature 
>>>>> stabilized crystal with 0.5ppm stability. To the 
>>>>> best of my knowledge this was a "state of the art" 
>>>>> implementation of automomous time keeping for 1979.
>>>>> 
>>> 0.5 ppm for boxes that get carried around in military 
>>> trucks and bounced around in the field -- that's quite 
>>> good.  For something that's sitting in a reasonably 
>>> controlled environment, that's not so great; 
>>> I think that 10^-8 would be considered state of 
>>> the art for OXCOs (1970s or not).
>>> 
>>> For autonomous timekeeping independent of technology, the 
>>> state of the art was a second per year or so (that's 10^-8, 
>>> roughly) around the early 1900s.  First with pendulum 
>>> clocks (Shortt clock), then around the 1940s or so crystal 
>>> clocks came in that could match this.  And not too long 
>>> after that there came the rubidium (10^-10) and cesium
>>> (10^-14) clocks.  Some of that would be found in military 
>>> gear, I think (Rb at least, Cs somewhat less likely).  
>>> Consider GPS satellites, which have either or both built-in.
>>> 
>>> 	    paul
>>>