[LEAPSECS] Civil timekeeping before 1 January 1972

Joseph Gwinn joegwinn at comcast.net
Fri Mar 13 10:10:55 EDT 2015

On Thu, 12 Mar 2015 18:50:56 -0700, Tom Van Baak wrote:
> I didn't think that NTP or POSIX or PTP is what we'd call a timescale. 

As discussed in other responses, a timescale requires only three 
things, a definition of zero time (or a specified time), a definition 
of the "second" (or some other time duration unit), and a progression 
rule.  That's it.

By this definition, all three (NTP, POSIX, PTP) define private 
timescales for their own internal use, and translate to and from 
external timescales as needed.

> NTP is a UTC synchronization algorithm. 

NTP is a synchronization algorithm for sure, but NTP is not limited to 
UTC, even though the RFCs speak of UTC.  Lots of people use NTP to 
distribute GPS System Time, and I bet that there are people now using 
NTP to distribute TAI.

> UT0 is a measurement. UT1 is a timescale. TAI is a timescale. UTC is a 

UT0 *is* a timescale, one that is tied to a specific astronomical 
observatory.  Multiple UT0 timescales are combined to yield UT1, and 
UTC is derived from UT1.

Joe Gwinn

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