Data Item _pdbx_reflns_twin.mean_F_square_over_mean_F2
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General 
- Item name
- _pdbx_reflns_twin.mean_F_square_over_mean_F2
- Category name
- pdbx_reflns_twin
- Attribute name
- mean_F_square_over_mean_F2
- Required in PDB entries
- no
- Used in currrent PDB entries
- No
Item Description
The ideal statistics for twinned crystals. The values calculated with the
acentric data are given below.
Statistic Untwinned data Perfect twinned data
<I2>/<I>2 2.0 1.5
<F>2/<F2> 0.785 0.865
References:
Yeates, T.O. (1997) Methods in Enzymology 276, 344-358. Detecting and
Overcoming Crystal Twinning.
and information from the following on-line sites:
CNS site http://cns.csb.yale.edu/v1.1/
CCP4 site http://www.ccp4.ac.uk/dist/html/detwin.html
SHELX site http://shelx.uni-ac.gwdg.de/rherbst/twin.html
Data Type 
- Data type code
- float
- Data type detail
- float item types are the subset of numbers that are the floating numbers.
- Primitive data type code
- numb
- Regular expression
- -?(([0-9]+)[.]?|([0-9]*[.][0-9]+))([(][0-9]+[)])?([eE][+-]?[0-9]+)?