Re: [art] Predictable Internet Time

[Joe Touch <[e-mail]>]

On 3/29/2017 7:53 AM, Philip Homburg wrote:
>> I know of no POSIX system with a cesium atomic clock.
>>
>> The issue is that POSIX really runs off of whatever local source of time
>> passage is available, and can (and does) drift from TAI on *each*
>> system. That drift can't be determined until your system tries to sync
>> with an external source (e.g., via NTP).
> To be completely pedantic, a single cesium clock will also drift from TAI/UTC.
>
> There is no such concept as being in sync with TAI without external
> corrections.

Yes - I got email off-list about this and need to update the doc to
remind us that TAI is actually determined post-facto, though its current
value is approximated.

> To be even more pedantic, of course that depends on the desired accuracy.
> A cesium clock could easily stay within one hour from TAI for a period of a 100
> years. A random PC with a quarz crystal at room temperature would have a hard
> time doing that.

Right - I will update the doc accordingly. AFAICT, POSIX time implies
(but never states) that it uses a local reference clock to emulate TAI.

Joe