Things to do at about 2005-12-31 23:59:60Z

From: Markus Kuhn <>
Date: Mon, 19 Dec 2005 23:31:22 +0000

Surely you are all very busy with last-second shopping for the many
forthcoming leap second parties later this month.

But what interesting things *are* there to do during a leap second?

I feel obliged to give the matter of appropriate geeky behaviour during
a leap second some thought, after having been tricked by a Nature
journalist last July into making a public statement to that end.

I suspect, the basic exercise will be running a little test routines on
various NTP-synchronized hosts, that log the progression of
clock_gettime(), gettimeofday(), etc. against whatever hardware counter
register is available, just to see what actually happens these days at
the API during a leap second with the very latest kernel versions.

What could show interesting effects during a leap second?

Of all the normal personal-computer applications, I suspect by far the
most clock sensitive ones may be streaming audio and video applications
such as

  - Mediaplayer
  - Realplayer
  - Quicktime
  - Software DVD decoders
  - VoIP (Skype, etc.)

followed by some types of networked computer games. It is very unlikely
that any standard computer application will actually display 23:59:60,
because the POSIX API has no way of communicating such a time stamp,
which can only be obtained using special leap-second aware system calls
such as adjtimex().

There are of course countless GPS, GLONASS, DCF77, WWVB, etc. receivers
to be watched, as well as applications that depend on them.

If you have a counter connected to the power grid, at least in most of
Europe (i.e., the UCTE 50 Hz network), you should see that -- thanks to
the leap second -- the frequency will during the following day be set
slightly lower, to ensure that European electricity consumers pay back
the free 50 cycles they got during the leap second. (But it may take a
few days of averaging until this long-term phase shift by 50 cycles
actually becomes clearly visible in the general phase/frequency noise of
the power grid.)

Owners of long-wave radios for the 40-70 kHz range with BFO, as well
as owners of shortwave radios, can listen to the additional leap second
pulse being transmitted by the relevant time and frequency stations, as
well as the DUT1 change immediately afterwards.

How about calling various speaking clocks all over the world and measure
how long it takes until they notice the leap second.

Will the BBC broadcast seven beeps at the end of this year, instead of six?

What about Big Ben?

What else could (or should) react to a leap second?

It might be fun to compile a comprehensive documentary here on how the
leap second is implemented in practice today ...


Markus Kuhn, Computer Laboratory, University of Cambridge || CB3 0FD, Great Britain
Received on Mon Dec 19 2005 - 15:32:20 PST

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