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, pp. 77-78

Section Definitions of single quantities

B. McMahona*

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

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Example[link] is the core dictionary definition of the data name for the ambient temperature during the experiment. Because this is a single (non-looped) value, the relevant data name is one among several discrete items in the DIFFRN category. No further description of its relationship to other data items is required.

Example A simple definition of a data item describing a physical quantity.

[Scheme scheme5]

The type of the associated data value (numb for numerical) is specified, together with any constraint on its legal value. The range specified ( 0.0:) indicates that it may be any non-negative real number. The physical units of the quantity are also indicated.

The _definition attribute is a concise human-readable documentation of the meaning associated with the data name.

Example[link] is taken from the powder dictionary and illustrates a data item that can have only one of a limited set of values. This data item indicates the geometry of the experiment. The associated data value is of type char and may legally take only one of the two possible values listed.

Example A data item that can take only one of a discrete set of allowed values.

[Scheme scheme7]

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