Almost Accurrate Clock

[Henry Spencer]

> 	The discussion of using the Heath WWV receiver as a clock brings
> a question to my mind. Does such a receiver used as a computer clock really
> win over using the 60Hz line frequency ? Although for any short period of
> time, if the receiver picks up WWV, its time keeping should be more accurate
> than using the 60Hz, it is my understanding that the power companies strive
> to make the long-range accuracy of the 60Hz signal very good. Whereas with
> the WWV receiver, there would be no mechanism to insure that time losses
> would be balanced by time gains. My current experience is that digital clocks
> operating off the 60Hz are more accurate on a month by month or year by year
> basis than most crystal-controlled watches.

This says more about the cruddiness of crystal-controlled watches than
about the accuracy of 60 Hz.  The 60 Hz signal normally is controlled
by reference to a precision crystal oscillator, better than the one in
watches but still just a crystal oscillator.  The WWV signal is derived
directly from the atomic clocks that are *the* time standard for the US
and are part of the collective time standard for the world.  You just do
not get timekeeping that is better than that.  The National Bureau of
Standards most assuredly puts more effort into accurate clocks than your
local power company does.  *Provided* that the Heathkit clock reliably
receives and decodes the WWV signal -- not entirely a safe assumption,
as DMR has related -- it's definitely a better time source.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry