PT Barnum was right

From: Steve Allen <sla_at_UCOLICK.ORG>
Date: Thu, 6 Jul 2006 07:27:56 -0700

In the this week is a press release for a clock that
automatically tracks leap seconds. The PR glowingly touts how the
clock traceable to NIST, so it is useful for timekeeping in all sorts
of processes that need ISO 9000 certification.
It goes on to say that the clock is always accurate to 1/10000 s.

The manufacturer has more to say
For less than $20 this battery powered clock is certified by an
ISO 17025 calibration laboratory accredited by A2LA.

But the only output is a liquid crystal display, and liquid crystals
have response times around 10 ms. That's 1/100 s, not 1/10000 s.

This seems akin to all the complaints about GPS receivers which
display a time that is off by about 2 seconds. I've never bothered
to dig on that, but my impression is that they probably also display
a position of where they were 2 seconds ago.

Finally, I've been spending a lot of time in the LA region lately.
The CBS radio affiliate in the SF Bay area broadcasts the hourly
national news spot on, and the time tone is useful for setting a
watch. The CBS radio affiliate in the LA area very plainly is using a
time compressing/FFT pitch shifting device on the live national feed.
The time tone in LA always happens around 10 to 15 seconds after the

Sometimes system delay is unintentional, sometimes it is intentional.
Even before PT Barnum latin had a two word phrase for such products.

Somebody tell me again -- why is it thta broadcast civil time signals
need atomic accuracy?

Steve Allen                 <>                WGS-84 (GPS)
UCO/Lick Observatory        Natural Sciences II, Room 165    Lat  +36.99858
University of California    Voice: +1 831 459 3046           Lng -122.06014
Santa Cruz, CA 95064     Hgt +250 m
Received on Thu Jul 06 2006 - 07:28:18 PDT

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