# Core CIF Dictionary version 2.3

# _reflns_Friedel_coverage

### Name

`'_reflns_Friedel_coverage'`
**Category:** reflns

**Data type:** numb

**Enumeration range:** 0.0 -> 1.0

### Definition

The proportion of Friedel related reflections present in
the number of the 'independent reflections' specified by
the item _reflns_number_total.
This proportion is calculated as the ratio:
[N(Crystal class) - N(Laue symmetry)] / N(Laue symmetry)
where, working from the _diffrn_refln_ list,
N(Crystal class) is the number of reflections obtained on
averaging under the symmetry of the crystal class
N(Laue symmetry) is the number of reflections obtained on
averaging under the Laue symmetry.
Examples:
(a) For centrosymmetric structures its value is
necessarily equal to 0.0 as the crystal class
is identical to the Laue symmetry.
(b) For whole-sphere data for a crystal in the space
group P1, _reflns_Friedel_coverage is equal to 1.0,
as no reflection h k l is equivalent to -h -k -l
in the crystal class and all Friedel pairs
{h k l; -h -k -l} have been measured.
(c) For whole-sphere data in space group Pmm2, the value
will be = 0, k >=0, l lead to the
same value as in (c), whereas measurements of the
two equivalent octants h >= 0, k, l >= 0 will lead to
a zero value for _reflns_Friedel_coverage.

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