[ntp:questions] A Suggestion For Abolishing the Leap Second

jlevine jlevine at boulder.nist.gov
Mon Jun 4 18:57:29 UTC 2007

> Picking a small nit: WWVB and other Time and Frequency Stations happily
> transmit a variety of frequencies for carrier and modulation. That's how
> I calibrate my radios.

   Sure. The audio tone bursts transmitted by WWV (and WWVH) could be
to anything. However, it would not be so easy to untangle the carrier
from the time code on WWVB. The time code generators for WWVB (and for
the GPS system, for that matter), assume that the frequency of the
and the chipping rate of the time code are locked together in some
relationship. This fixed relationship is buried pretty deeply into the
and I would guess that it would be quite difficult to change the
length of the
transmitted second without changing the frequency of the carrier and
chip clock.

> Last we talked you said the goal of Ultimate Timekeepers of the World
> was to the nanosecond using Two-Way Satellite Transfer. The NIST method
> used to wrangle an unruly herd of cesium clocks is described in my book.
> The method provides nominal time and frequency offsets between all
> clocks in the herd and establish a nominal laboratory timescale. I call
> this NTP distributed mode and have threatened to implement it.

   Absolutely. The frequencies of our internal ensemble of clocks can
by as much as  1e-11 from the frequency of TAI or UTC. However, if I
an offset this large to escape from the clock room I would be sent to
bed without
dinner for a month. Our serious customers expect (and pay for)
fractional frequency
stabilities on the order of 1e-14 or 5e-15. These frequencies
to time dispersions on the order of nanoseconds per day.
> A review of the IERS data from 1961 to 1972 shows periodic ephemeris
> time (ET) offsets declared in both time and frequency. That must have
> driven the microsteppers bonkers.

   You have no idea. As the guy who was out there where the rubber
the road, it was absolutely crazy.

>  If I could reinvent the world, I would run the master clocks in barycentric
>  time and distribute offsets via the web. This is TAI at the mass center
>  of the solar system where the gravitational potential is zero.

   Yes, this idea was proposed some time ago, and it is currently
pushed pretty hard by the folks who need to plan for going to Mars.
version of this idea will probably be adopted if/when space travel
more common. However, the idea that the rotating geoid (which is the
basis for the current SI defintion) is the center of the universe will
be easy to overcome.

> You and I discussed whether NTP should retail TAI (as in POSIX) or UTC
> and for a number of reasons decided on UTC.

   At least for now, I would stick with that decision, since UTC is
closer to
the definition of legal time and the financial world does not
understand TAI
and would certainly not want more ambiguity in the time stamp.

Judah Levine
Time and Frequency Division
NIST Boulder

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