[LEAPSECS] Civil timekeeping before 1 January 1972
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.
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