From: Alan R. <ala...@gm...> - 2011-04-06 13:24:14
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On Wed, Apr 6, 2011 at 4:24 AM, Erick Antezana <eri...@gm...> wrote: > Hi, > > that change might have, first of all, an impact in the mind of my > users since they are already used to deal with two types (categories) > of units: basic/base and derived, being basic (for us) the original > terms under 'base unit' plus the ones we added to that branch (e.g. > foot) --independent of any system. and being ''derived unit' the terms > made up by taking the base ones (e.g. square foot) or a bit more > "complex" such as 'kilogram per cubic meter'. What was the original > definition of those terms (basic unit and derived unit)? base unit: A unit which is one of a particular measure to which all measures of that type can be related derived unit: A unit which is derived from base units. Any of the units of the same measure could be the base unit as they all can be related to each other. Which one is base depends, as I mentioned, on convention. By (the intended sense of) this definition of derived unit, foot would be a derived unit if meter is the base unit, as would your example k/m^3. But even the units that are written as equations on units of multiple measures are not unambiguously derived units - the only requirement is that (according to NIST) that the quantities they measure are mutually independent. For example which electrical unit is chosen is a matter of conventions (current, voltage, resistance) and then the others are derived. > On the other hand, this also has an impact (relatively minor) in the > application (under construction) that is supposed to deal with the > conversion of units (e.g. degree Celsius into Fahrenheit)... Don't know if you've discussed your approach here, but I know that there are several people who have takes on how to do this - ccing Sivaram Arabandi and Melanie Courtot as they have both expressed opinions. Perhaps there's an opportunity to collaborate... -Alan > > Alan, I was not able to get your slides from your dropbox ... can you > share them in a different way? > > cheers, > Erick > > On 5 April 2011 19:36, Alan Ruttenberg <ala...@gm...> wrote: >> Whether a unit is derived is always relative to a particular system. >> So a derived unit in cgs is different from a derived unit in si. You >> might have a look at my presentation - http://tinyurl.com/3egxlln >> >> Without qualification it's confusing and unhelpful. >> >> I'm curious whether the change impacted your work, and exactly how. >> >> Thanks, >> >> -Alan >> >> On Tue, Apr 5, 2011 at 9:48 AM, Erick Antezana <eri...@gm...> wrote: >>> Hi, >>> >>> I was wondering why 'derived unit' ( UO:0000046) has been "obsoleted"? >>> >>> Also, the 'base unit' children were "upgraded" and are now direct >>> children of 'unit'... >>> >>> cheers, >>> Erick >>> >>> ------------------------------------------------------------------------------ >>> Xperia(TM) PLAY >>> It's a major breakthrough. An authentic gaming >>> smartphone on the nation's most reliable network. >>> And it wants your games. >>> http://p.sf.net/sfu/verizon-sfdev >>> _______________________________________________ >>> Obo-unit mailing list >>> Obo...@li... >>> https://lists.sourceforge.net/lists/listinfo/obo-unit >>> >> > |