Editing Module:Convert/documentation/conversion data/introduction (section)

=== Default ===
A default is a code for a unit or combination that identifies the output unit or units that will be used if none is specified in the convert template. The [[#Defaults|Defaults]] section defines exceptions for unit codes with an SI prefix, where the default output is different from that of the base unit. Also, units using [[#Engineering notation|engineering notation]] may appear in the defaults section to define a default output for the unit.

A default may specify a unit code or an expression that tests the input value, and which produces one of two different outputs depending on that value. In the expression, <code>v</code> represents the input value specified in the convert template, and exclamation marks (<code>!</code>) are used to separate the expression into either three or four fields. For example, the following expression might be used as the default for unit <code>in</code> (inch):
: <code>v < 36 ! mm ! cm</code>
The first field is a condition which evaluates to ''true'' or ''false''. In this example, if the input value is less than 36, the default output unit is <code>mm</code>; otherwise, it is <code>cm</code>.

If present, the fourth field is appended to the result. For example, the following expression might be used for unit <code>Ml</code> (megalitre):
: <code>v < 28.316846592 ! e3 ! e6 ! cuft</code>
If the condition is true, the result is <code>e3cuft</code>; otherwise, it is <code>e6cuft</code>.