[time-nuts] 2015 Leap Second

Tom Van Baak tvb at LeapSecond.com
Sat Jan 24 16:34:52 EST 2015

Hi Chuck,

Thanks for the comprehensive list. Very nice work. This bug in many versions of the HP SmartClock-series has shown up before (but not always in the 90's, see below). What's going is yet another problem with how developers write code for leap seconds. It's really hard to get right.

There is a distinction between when leap seconds are *announced*, usually 2 to 6 months in advance (somewhat variable, almost random) and the month in which a leap second actually *occurs* (a very specific instant).

Unfortunately, the word "pending" is ambiguous since it does not distinguish between the casual advising that a leap second will occur many months in the future and the actual month in which the leap second occurs. This leads to both human and technical confusion.

In addition, there is confusion about when a leap second *can* occur. The UTC specification implies a leap second may occur at the end of any month, although it is most likely the 6th or 12th month, and if not that, the 3rd and 9th month. Some vendors have misinterpreted this to mean, for example, that if a leap second is announced in January it will therefore occur in March (rather than June). Oops.

These are difficult bugs to fix. For most of the 70's, 80's and 90's leap seconds were announced only a few months ahead of time. But in the past decade, IERS had been able to predict leap seconds almost 6 months in advance -- and this exposes bugs in software that used to work just fine.

  ----- Original Message ----- 
  From: Charles Zabilski 
  To: Tom Van Baak 
  Sent: Saturday, January 24, 2015 9:47 AM
  Subject: 2015 Leap Second


  Unfortunately I no longer receiver emails from time nuts due to my @yahoo.com email address.  In response to your desire to pull together a list of GPS receivers' handling of the upcoming leap second, please see the following:

  Receiver        1st Reported date        Reported Leap Sec Date
  Z3801A               22 Jan 2015                    31 Mar 2015
  Z3811A               22 Jan 2015                    31 Mar 2015
  Z3816A               22 Jan 2015                    31 Mar 2015
  58503A               22 Jan 2015                    31 Mar 2015
  58503B               22 Jan 2015                    31 Mar 2015
  59551A               22 Jan 2015                    31 Mar 2015

  Z3805A               No Leap Second Indication
  Z3815A               No Leap Second Indication

  Please note that I usually only check for the leap second notifications in the mornings.  In all probability the notifications occurred some hours earlier.  Also, I am communicating with the GPS receivers through the external Com port using my GPS Control Program and not examining the internal GPS module data stream.

  I hope this is of some assistance.

  Chuck Zabilski
  BD Systems, Inc.
  Evergreen, CO

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