Subject: Leap Second Questinnaire

From: Demetrios "N." Matsakis <[email-masked]>
Date: Mon, 24 Jan 2000 22:15:21 +0000 (UTC)

Dear IETF member,

Several months ago, I sent out the following questionnaire concerning
the possibility that leap seconds might be discontinued (a discussion of
the reasons is provided at the end).  The original request asked for a response 
by January 15, but we are extending that so as to reach a larger 
constituency, such as the IETF.

I am anticipating that this will be distributed via an email exploder,
and would appreciate a response by anyone interested by February 15.

Although all responses will be tabulated, we are most interested in 
finding verifiable specific practical show-stoppers such as "system X would 
require Y million dollars to be reprogrammed, and you have our permission to 
identify it publicly".

I also would prefer to receive responses in ascii, as opposed to attachments.

Thank you,

Dr. Demetrios Matsakis

*************************************************************************

Dear Project Manager or Scientist,

It is being proposed to change the definition of Coordinated Universal
Time (UTC) regarding the insertion of leap-seconds, possibly even
eliminating their use.  The issue has been discussed in several 
timekeeping forums, and published in the Innovations Section of the 
November, 1999 issue of GPS World.  

Leap seconds are introduced so as to keep UTC synchronized (within 0.9 s) 
to the time scale determined from the Earth's rotation.  Should no new 
leap seconds be inserted, solar time will diverge from atomic time at 
the rate of about 2 seconds every 3 years, and after about a century 
|UT1-UTC| would exceed 1 minute.  Although no fundamental problems are 
anticipated, it is very likely that Y2K-like problems may result in 
software that assumes UT1=UTC, or |UT1-UTC|< some value, or whose 
input/output records use a field size that can only accommodate 
|UT1-UTC| values up to one second.
 
To gather information, an URSI Commission J Working Group was formed,
consisting of Don Backer, Wim. N. Brouw, Barry Clark, Irwin Shapiro,
Ir. E. Van Lil, and myself.
 
We would like to ask you to consult with the members of your institute
who currently deal with UT1-UTC, and give us a considered response to
the following two questions:
 
A. If the appropriate international bodies decide to eliminate the
insertion of new leap seconds, would you foresee any practical problems
for your institution/instrument/observations?
 
     no  ____

  *  yes ___
 
  *  possibly ____
 
     (* please explain any known or possible problems, but if possible 
        try to answer in ascii text instead of an attachment)
 
B. Would you be in favor of such a proposal?
 
     yes ____
 
     no  ____
 
     indifferent ___

     have better idea ___
 
     (feel free to comment)

C. Is there anyone else you would recommend we contact?
    (feel free to forward this email directly)
 
I would appreciate your assistance, and a response by January 15 to
[email-masked].

This questionnaire was first sent to the URSII national representatives,
a list of 931 astronomical institutions maintained by the American
Astronomical Society, and 125 prominent scientists.  It has since sent
sent to several mailing lists associated with Earth rotation.  I would 
like to apologize to anyone contacted twice, but also appreciate it if 
you would forward this email to anyone we may have missed.  We will
tabulate all responses, and are particularly interested in quantitative 
estimates from people whose systems can not easily accommodate the change.
Unix technology permitting, I will also email the report to all who have
responded.

Sincerely,
 
Demetrios Matsakis
________________________________________________________________________
Dr. Demetrios N. Matsakis            Director, Time Service Department
(202) 762-1587  DSN 762-1587         U. S. Naval Observatory
FAX (202) 762-1511                   3450 Massachusetts Avenue NW 
[email-masked]              Washington DC, USA  20392-5420
________________________________________________________________________

**********************************************************************

Below is the "standard response" I have been giving to responders.  It
seems more appropriate to provide it in advance:

Thank you for your response, which will be tabulated.  Unix-technology
willing, we also plan to send a copy of our report all responders. 

Many people have asked me why there is a move to rethink the leap seconds,
with solutions such as (but not limited to) adding no new leap seconds.
I unfortunately edited out some of the reasons from early drafts of the 
questionnaire, because I was afraid that people would not read a long email.  
Since then, I have developed the following "standard reply":

1.)  Many high-tech navigation systems, can't handle leap seconds very well.  
GLONASS, the Russian equivalent to GPS, goes off-line for leap second 
adjustments.  Also, problems can occur in interfacing between systems that 
handle leap seconds differently.  There is also the practical problem of 
inserting a second every year and half - people often do it the wrong way.  
The response one person sent me is below, and it concerns Network Time 
Protocol (NTP), which uses the internet to transfer time.

> If leap seconds went away, the NTP community would worship the ground you
> walk on. Leap secs introduce a manual discontinuity in the NTP time scale.
> It takes a while to propagate leap secs through the hierarchy. Leap seconds 
> are a tremendous headache in the NTP world because they cannot be predicted. 
> One must set a flag to indicate that one is coming. I think it is a very
> true statement that all GPS users would vote against continuing leap seconds,
> not just NTP users. Many telecommunications circuits use GPS or atomic clocks
> to keep cellular phones in operation, and leap seconds are a nuisance to them
> as well. 

2.) I also received many comments about the effects on society when UT1
diverges.  Note that we are talking about a minute in the next century.  
Society routinely handles a one-hour switch with every daily savings time, 
and a half-hour offset if they live at the edge of a time zone.  By
the time leap seconds add up to an hour, the world will be very different.
If we have settled the solar system, a whole new scheme will probably
have evolved.  Even if we have not changed our system, society has 
enough slop in its timekeeping that people will slowly shift without even 
knowing it.  More people will start showing up to work at 9:00 AM, and less at 
8:30 AM, etc.

3) The "innovations" section in November's GPS World is on this subject,
and discusses other possibilities aside from "no new leap seconds".  These 
are inserting larger discontinuities less frequently, inserting integer
leap seconds at predefined times, simply using TAI, and redefining
the length of the second.

4) It should be pointed out that UT1-UTC is readily available on the web.
The USNO, as a subbureau of the International Rotation Service, makes
this information available via a weekly mailing and from a web page
at http://www.maia.usno.navy.mil, and other organizations also provide
this service.

5) My final comment is not to worry about any "surprise" decisions - before/if 
the international bodies all decide to do this, it will be fully debated and 
publicized.  My role, here, is simply to gather information.