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In article <1990Jan10.175719.8720@haven.umd.edu> louie@sayshell.umd.edu (Louis A. Mamakos) writes:

#As far as the Heathkit "Most Accurate Clock", well, its not.  The
#RS-232 interface has some severe problems which precludes its
#effective use to those persons that want accuracy in the millisecond
#regime.  If you're looking for somethat that's accurate to within a

Could you elaborate on this?  It seems from the Heathkit specs that
all what it amounts to is a fixed and predictable time difference between
displayed time and the leading edge of the RS232 output, which can be
compensated for in the computer - e.g. by waiting for the minute interrupt
and then setting the clock seconds to 1.3 or whatever it amounts to.

Heath states that the clock display is accurate within 10 milliseconds.
If that holds up, it should be a simple matter to calculate the
display-to-interrupt time difference based on baud rate, computer and
Heathkit RS232 generators; or just measure it with a scope.
If the RS232 output is systematically 1 second behind the display (as
has been rumored for some early board revisions), then that can be added
to the constant.

It is true that you can get better clocks than 10 ms.  But that is not
a problem with the RS232 interface but is inherent to the time signal.
It begins to get iffy to verify that you are in sync with the Master
Clock (in France) anyway.

You also have to distinguish between relative and absolute accuracy.
The relative accuracy is what matters to most people.  Heath clocks do
that very well.

Torkil Hammer.