[#mp_units-named_constant-02]
= xref:mp_units.adoc[mp&lowbar;units]::xref:mp_units/named_constant-03.adoc[named&lowbar;constant]&lt;Symbol, U, RSU&gt;
:relfileprefix: ../
:mrdocs:

Specialization for a measured constant declaring its relative standard uncertainty

== Synopsis

Declared in `&lt;mp&hyphen;units&sol;framework&sol;unit&lowbar;definitions&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template&lt;
    xref:mp_units/symbol_text-032.adoc[symbol&lowbar;text] Symbol,
    xref:mp_units/Unit.adoc[Unit] auto U,
    typename M,
    xref:mp_units/relative_standard_uncertainty.adoc[relative&lowbar;standard&lowbar;uncertainty&lt;M&gt;] RSU&gt;
requires (!Symbol&period;empty()) &amp;&amp; detail&colon;&colon;magnitude&lowbar;is&lowbar;positive&lt;M&lcub;&rcub;&gt;
struct xref:mp_units/named_constant-03.adoc[named&lowbar;constant]&lt;Symbol, U, RSU&gt;
    : ::&lowbar;base&lowbar;type&lowbar;
----

== Description

The same as the above but additionally stores the relative standard uncertainty of a constant that is measured rather than exact by definition&period; The value transcribes the entry published in the source metrology table (e&period;g&period;, CODATA)&period;

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `::&lowbar;base&lowbar;type&lowbar;`
| 
|===

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:mp_units/named_constant-02/_base_type_.adoc[`&lowbar;base&lowbar;type&lowbar;`] 
| Exposition&hyphen;only alias naming this specialization&apos;s base type&period;
|===


== Static Data Members

[cols="1,4"]
|===
| Name| Description
| xref:mp_units/named_constant-02/_relative_standard_uncertainty_.adoc[`&lowbar;relative&lowbar;standard&lowbar;uncertainty&lowbar;`] 
| The wrapped relative standard uncertainty magnitude
| xref:mp_units/named_constant-02/_symbol_.adoc[`&lowbar;symbol&lowbar;`] 
| Unique constant identifier
|===


== Template Parameters

[cols="1,4"]
|===
| Name| Description
| *Symbol*
| a short text representation of the constant
| *Unit*
| a unit that we use to define a constant
| *RSU*
| the relative standard uncertainty of the measured value
|===


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