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On Mon, Apr 13, 2015 at 10:45 AM, Alexander Belopolsky <alexander.belopolsky@gmail.com> wrote:

Am I wrong, or is this a semantic question as to what "wall" time means?

You are right about what wall() means, but I should have been more explicit about knowns and unknowns in the wall(loc, t) = lt equation.

In that equation I considered loc (the geographical place) and lt (the time on the clock tower) to be known and t (the universal (UTC) time) to be unknown. A solution to the equation is the value of the unknown (t) given the values of the knowns (loc and lt).

The rest of your exposition is correct including "a given UTC time maps to one and only one 'wall time' in a given timezone." However, different UTC times may map to the same wall time and some expressible wall times are not results of a map of any UTC time.

got it. I suggest you perhaps word it something like:

wall\_time = f( location, utc\_time)

and

utc\_time = f( location, utc\_time )

These are two different problems, and one is much harder than the other! (though both are ugly!)

you can, of course shoreten the names to "wall" and "utc" and "loc" if you like, but I kind of like long, readable names..

-Chris







--

Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
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Chris.Barker@noaa.gov