Re: Predictable Internet Time

Stewart Bryant <stewart.bryant@gmail.com> Tue, 03 January 2017 18:30 UTC

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Subject: Re: Predictable Internet Time
To: Cyrus Daboo <cyrus@daboo.name>, Phillip Hallam-Baker <phill@hallambaker.com>
References: <CAMm+LwgfQJ8aG5wB=d3fRbbeje3J9o7Z4_DCuP8DL88ouDeKzw@mail.gmail.com> <504e2cea0d1668c31486b05fec0a967a4446aefe@webmail.weijax.net> <CAMm+Lwi_jU6gjdtdM6a2n_9_89tUvWBNXxnMtSjTEA++h1D4Ew@mail.gmail.com> <e0a43370-751f-808c-3719-9716f9cd57d1@isi.edu> <alpine.DEB.2.11.1701031348430.7102@grey.csi.cam.ac.uk> <0bbfcd7c-11a7-0e7f-56f7-eee959b7a947@gmail.com> <CAMm+Lwi0sQyRE_2dMCkwTk7xTiK2JbHhHSPYMkdG2FeBw_6CNA@mail.gmail.com> <7BDE58D23ADF3BC046F8942D@caldav.corp.apple.com>
From: Stewart Bryant <stewart.bryant@gmail.com>
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Date: Tue, 3 Jan 2017 18:30:19 +0000
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On 03/01/2017 18:03, Cyrus Daboo wrote:
> Hi Phillip,
>
> --On January 3, 2017 at 12:42:42 PM -0500 Phillip Hallam-Baker 
> <phill@hallambaker.com>; wrote:
>
>> 1) TAI: Use this and only this for any and all purposes that involve
>> recording the time an event took place. Including forensic and 
>> scientific
>> purposes.
>>
>> 2) PIT: Use this for inter-machine communications. It may also be 
>> used to
>> present TAI in a human readable form because the mapping from TAI to PIT
>> is fixed.
>>
>> 3) Local Time Zones: For human display purposes
>
> Please note that local time is needed not just for human display 
> purposes but also for handling recurring events that are "anchored" to 
> a local time. e.g., you want your thermostat to turn on at 6pm local 
> time every day, but that has to account for daylight saving time 
> changes etc. Thus when defining future data/time values, often (local 
> time & time zone id) is required and must be part of the data 
> interchange between devices. Thus the need to keep devices up to date 
> with time zone changes (which was the primary impetus for the tzdist 
> RFC7808 work).
>

Only the UI needs the TZ information, the machine can operate just fine 
with any timescale. That is you present the time in local time, but 
operate in global time, and this is definitely an application that will 
not care about leap seconds.

- Stewart