## DATETIME@C4VLPLISTSERV01.LOC.GOV

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Re: Extended Interval (L2 )

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Thu, 22 Oct 2015 18:15:18 +0200

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 ```On Thu, 22 Oct 2015 09:44:27 -0400, Denenberg, Ray wrote > > I also have difficulty explaining the difference between 'xx' and 'uu': > http://www.loc.gov/standards/datetime/pre-submission.html#maskedprecision > "Note the difference in semantics between 'x' and 'u'. '196x' has decade precision while '196u' has year precision. Both represent an unspecified year during the 1960s, but for 196x the year is not supplied because it is known only with decade precision. In contrast, for 196u the year is not supplied for reasons that are not specified but there is some expectation (though no guarantee) that the year may be supplied later; for 196x there is no such expectation." > That does sum it up. What is so hard? Instead of dates/time I think we are better off thinking of temperature or weights. They are an area where I think we are much more accustomed to thinking in precision. How much does the object weigh? 2x grams versus 2u grams. The former means that the object weighs on a scale that can only read 10g (say a balance where we have only 2 nickels to measure against, e.g. 2x5g objects). That later says that we guess it is around 20-29 grams but expect to measure it with a gram scale and finalize its value.. How do we in weights specify gram precision? 2g How do we specify that something is 2g measured to mg precision? 2.000g And 2g to centigram precision? 2.00g In weights.. The number 1xx means I've tagged the weight as some weight in the range 100 to 199 and expect to fill in the numbers once I place them on the balance. The x is just a placeholder for missing infomation. The number 1uu means something else.. In weights and lengths we have units to help with our specification. ng, mg, g, hg, kg, ton, etc. and nm, mm, cm, m, km, hm, km,.... 1uu mg is really 1 g. 1xx is NOT 1g. In scientific expressions we have +- to specify precision since not everything fits in 10s. In time we have ns, ms, s, min., hours, days etc. But what do we have with days? Months? Years? Decade, Century, Milennium, .. When someone says "gosh I have not eaten one of those for a decade" they don't mean that the last time they ate one was exactly 315576000 seconds ago. Now the tricky bit and pop-quiz! If uu is a century xu is a decade in a to be specified decade and xx is a year in a to be specified year and decade. What does "ux" mean?   > However I'm going to try to defer that discussion for now. > > Thanks. > > Ray -- Edward C. Zimmermann, NONMONOTONIC LAB ```