Tables for
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

International Tables for Crystallography (2006). Vol. G, ch. 3.1, p. 83

Section Units

B. McMahona*

aInternational Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England
Correspondence e-mail: Units

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As with data files described by DDL1 dictionaries, the physical unit associated with a quantitative value in a DDL2-based file is specified in the relevant dictionary. There is no option to express the quantity in other units. However, DDL2 permits a dictionary file to store not only a table of the units referred to in the dictionary (listed under _item_units_list.code and the accompanying descriptive item _item_units_list.detail), but also a table specifying the conversion factors between individual codes in the _item_units_list.code list. In principle, this allows a program to combine or otherwise manipulate different physical quantities while handling the units properly.

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