[LEAPSECS] Crunching Bulletin B numbers (POSIX time)

Richard Langley lang at unb.ca
Wed Feb 23 07:30:53 EST 2011

The mention of the needs of the military for precise/accurate time
reminded me of an article in my GPS World column from a number of
years back. I've put it and Judah Levine's article on the legal
traceability of time on our website:



-- Richard

On 22-Feb-11, at 5:43 PM, Warner Losh wrote:

> On 02/19/2011 16:23, Ian Batten wrote:



>>>> I think that before conjecturing the requires of isolated

>>>> machines which have no source of leap seconds (not even manual

>>>> application via a commandline interface "leap_next_31_dec") and

>>>> yet are attached to better than 0.02ppm clocks, someone should

>>>> provide an example of an isolated machine that is attached to a

>>>> 0.02ppm clock. And why everyone else should deal with the

>>>> complexity to save that one computer the $100 bill for a GPS

>>>> receiver.


>>> The issue isn't money, it's access to the sky.


>> WWV, MSF or DCF77.


>> If people need to operate machines in Faraday Cages, but are not

>> prepared to supply a single manual update of one bit of information

>> per six months, I'm not sure to what extent the rest of the

>> community should have to engage in huge complexity in order to

>> pander to them.


> WWV, MFS and DCF77 do not publish a list of leap seconds, nor the

> current UTC-TAI offset. In addition, they are unauthenticated

> sources of data. Many government/military applications require a

> source of time you can trust, not one that happens to be available

> that the enemy could jam/rebroadcast.


> GPS + SAASM gives you that, but you still have to wait for the

> almanac to know utc time. For hot systems, that data can be

> cached. For cold spares, you wait between 10 and 20 minutes to get

> it.


> Warner

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| Richard B. Langley E-mail:

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