[tz] Anecdotal discrepancy for Navajo nation in Arizona

Paul_Koning at dell.com Paul_Koning at dell.com
Thu May 26 20:01:12 UTC 2016

> On May 26, 2016, at 3:38 PM, Guy Harris <guy at alum.mit.edu> wrote:
> On May 26, 2016, at 6:36 AM, Deborah Goldsmith <goldsmit at apple.com> wrote:
>>> So, by "However, he observed that the parts of the Navajo nation adjacent to Page were actually observing the same time zone as Page (America/Phoenix, DST not in effect).", do you mean "if he went to parts of the Navajo nation adjacent to Page, his phone reported DST not being in effect" or "if he went to parts of the Navajo nation adjacent to Page, the clocks he saw reported DST not being in effect"?
>> The latter: residents of the Navajo nation (adjacent to Page, at least) were not using DST; they were using the same time as Page. My colleague did not directly observe their clocks, just what the residents said their clocks were.
> So they might just be ignoring the Navajo nation's rules and using their neighbor's rules instead; I think that's done elsewhere as well, near time zone boundaries (I think there may be cases where a location that's far from other places in its own time zone, but close to a location in another time zone, sets its clocks as if they were in the other time zone).

It may also be a technology issue.  Clearly modern smartphones can use shapefile data and their onboard GPS to derive timezone offset from the location, and possibly some do.  But I gather from earlier messages today that cell base stations also send their offset.  Obviously, a phone that relies on the base station to supply offset will have the wrong answer if it is in a different zone than the base it happens to be listening to right now.  It would not be a surprise if the "near Page" example is caused by this cell tower issue.

All these anecdotes suggest the need to verify that the rules as we believe them to be defined are indeed correctly understood.  But when there are officially stated rules, from authorities that have jurisdiction, those are the ones to use even if some real-world users don't follow those rules.  Otherwise we get to the point where your timezone is a matter of opinion, which is a lack of principle all too prevalent in too many other human activities...


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