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Re: Permitting new physical units?

  • To: Multiple recipients of list <coredmg@iucr.org>
  • Subject: Re: Permitting new physical units?
  • From: Howard Flack <Howard.Flack@cryst.unige.ch>
  • Date: Mon, 2 Mar 1998 09:30:18 GMT
> Whatever happened to the day of rest?

  You did not miss anything, the snow is absolutely horrid. I carried on
wiring up the decorative lamps on the signals, level crossings,etc on
the vintage train layout.

> Joergen prefers the generic approach because he considers it to be more 
> intuitive

  I agree. We do not want _xd_ _nd_ _ed_ as in Syd's multiple definition
example.

> 
> These items can be easily redefined as... and this is an example for
> all of the electron-dependent items listed above.

> ;   The largest, smallest and root-mean-square-deviation, of the
>     density in the final difference Fourier map. The *_rms value 
 
would be better as:

 ;    The largest, smallest and root-mean-square-deviation values of the
      difference density. The *_rms value 

Now in
> data_refine_diff_density_
>     _units_construct            (_diffrn_radiation_scat_units)_A^-3^   

  what happens to the person who does not use the A? The answer seems
obvious, I admit, but taken with

>     _example                   (_cell_length_unit)^3^ 

  seems to mean that you are likely to find yourself having to define an
_unit item for very many data items in the whole dictionary (i.e. one
for cell length, one for bond length, one for wavelength etc). How does
this construct take account of the powers of 10? e.g. mm and m are fine
for measuring physical lengths around the home or lab but cubed are
hopeless for volumetric measurements.

  Do I understand correctly that in this approach the units are an
attribute of the data name rather than an attribute of its instance as a
numerical value?

  I definitely agree that the multiple definition approach is the wrong
way.


Best wishes,
  H.


-- 
Howard Flack        http://www.unige.ch/crystal/ahdf/Howard.Flack.html
Laboratoire de Cristallographie               Phone:(+41 22) 702 62 49
24 quai Ernest-Ansermet             mailto:Howard.Flack@cryst.unige.ch
CH-1211 Geneva 4, Switzerland                   Fax:(+41 22) 781 21 92

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