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DATETIME  October 2015

DATETIME October 2015

Subject:

Re: 1/27 conference call notes: Long Year

From:

"Byrd, Donald A." <[log in to unmask]>

Reply-To:

Discussion of the Developing Date/Time Standards <[log in to unmask]>

Date:

Thu, 29 Oct 2015 00:18:56 +0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (38 lines)

Two comments on your notes on Long Year. First, FWIW, I think the committee's preference for keeping the exponential form is justified. True, very few people are likely to care about it, but for some uses, it'd be hard to do without. I'm thinking mostly about cosmology. The duration of the Stelliferous Era (time during which stars will shine) is about 10^14 years; the decay time for a supermassive black hole of ca. 10^11 solar masses due to Hawking radiation is estimated to be 10^100 years; etc. Extremely long time intervals also occur in science fiction.

Second, using "A" for precision because it suggests the word "accuracy" bothers me quite a bit. There's already way too much confusion between precision and accuracy! How about "Q" as the first available letter after "P"? I don't think 8601 uses "Q" for anything.

--Don


On Oct 28, 2015, at 2:21 PM, "Denenberg, Ray" <[log in to unmask]> wrote:

> The TC154 Committee developing 8601 Part 2 held a conference call yesterday. Following is a report on several issues of interest to us.
> [---- SNIP ----] 
>  
> Masked Precision
> In the current  EDTF spec, 'u' is a replacement character, or “placeholder”, as in '19uu', used for "unspecified".  'x' is a replacement character, as in '19xx', used for "masked precision".  As expected I have a difficult time explaining the difference.  But I cited the following (from a 2011 message)
>  
> Imagine, for example, two people that measure the weight of same specimen using different scales. One person using a good quality analytic lab balance- -- for example readable to 0.01mg with 0.05mg repeatability--- may read 1.0146g while the other using a much cruder scale readable to gramms may read only 1 gram. 1.0146g is not a greater measure than the 1g. Both have measured the same sample but at different precisions. The weights must then be "the same". Measuring another specimen the first reads on their analytic balance 1.0370g. The second person reads 1 gram. At the precision of the lab balance the second sample is heavier than the first but at the precision of the crude scale the two weigh the same.  Turing now to dates the date "1964-04" if measured in year precision would yield "1964". In month precision "1964-04" is before "1964-06" but in year precision they are "the same" just as two babies born on the same day but at different times share the same birthday.
>  
> The scale example is a good explanation of precision.  But the leap to dates is hard to grasp. When you say  ‘Turing now to dates the date "1964-04" if measured in year precision…’ , there is an implied “scale” analogy that measures time rather than weight.  We need to have a better understanding of how time is being measured.
>  
> Long Year – Exponential Form
> Recall there was discussion among us to eliminate the exponential form, though to retain the precision component. Thus instead of
> y17101e4p3  (Some year between 171000000 and 171999999, estimated to be 171010000  - 'p3' indicates a precision of 3 significant digits.)
> It would be
> Y171010000P3
> However, the committee prefers to retain the exponential form.
>  
> Furthermore, ‘P’ cannot be used, as it is already used within 8601 (for “period”).  Instead, ‘A’ is suggested (for “accuracy”).
>  
> [---- SNIP ----]
>  

---
Donald Byrd
Woodrow Wilson Indiana Teaching Fellow
Adjunct Associate Professor of Informatics
Visiting Scientist, Research Technologies
Indiana University Bloomington

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