[time-nuts] [LEAPSECS] Leap second to be introduced at midnight UTC December 31 this year

Heiko Gerstung heiko at am-anger-1.de
Fri Jul 22 05:45:08 EDT 2016

Am 22.07.2016 um 10:44 schrieb Martin Burnicki:
> Tom Van Baak wrote:
>> Time to mention this again...
>> If we adopted the LSEM (Leap Second Every Month) model then none of
>> this would be a problem. The idea is not to decide *if* there will be
>> leap second, but to force every month to have a leap second. The IERS
>> decision is then what the *sign* of the leap second should be this
>> month.
> Although this approach sound good, it would cause major problems for
> users of the German longwave transmitter DCF-77. The data format only
> has a "leap second pending flag", which means a leap second is to be
> inserted. AFAIK there is no spec to announce a negative leap second via
> DCF-77.
> Martin

I agree that LSEM seems like a good idea to get rid of the problem that leap seconds are happening not often enough to be in everyone's mind.

And I also agree that handling these monthly leap seconds would not adding complexity because you have to handle the occasional leap second anyway.

However, I believe that LSEM is not a good idea because of two things:
First, you would dramatically increase the efforts to distribute leap second announcements. At the moment a leap second announcement is announced roughly 6 months in advance, allowing to update devices in the field within a reasonable window of 4-5 months before the event. Doing it every month requires more frequent updates of lots of systems that currently have no connection to a leap second announcement information source like GPS or the Internet.

The second point is that the difference between solar time and UTC, which seems to matter at least to a considerable amount of people, is going to be higher compared to the current handling of leap seconds. If the IERS happens to determine that the Earth rotation speed was pretty constant last month and the time difference has increased only a few milliseconds since last month, you consciously have to increase it to one second minus the small actual difference. And then, in the next month, you have to basically jump back again.

Clearly getting rid of the leap seconds is the solution that requires the lowest effort both in terms of costs and technology. You do not have to touch a single device if you just keep the number of leap seconds constant from now on. With LSEM you have to touch probably 99% of all computer systems (their OS and possible applications) and at least 90% of all GPS receivers and clocks using other technologies.

And: the failure to get rid of this thing in the past should teach us how easy it will be to convince the ITU and the governments of the planet to change the current practice and go for LSEM.


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