doc/groff.html.node/Default-Units.html


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Previous: <a href="Motion-Quanta.html" accesskey="p" rel="prev">Motion Quanta</a>, Up: <a href="Measurements.html" accesskey="u" rel="up">Measurements</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Request-Index.html" title="Index" rel="index">Index</a>]</p>
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<h4 class="subsection" id="Default-Units-1">5.3.2 Default Units</h4>
<a class="index-entry-id" id="index-default-units"></a>
<a class="index-entry-id" id="index-units_002c-default"></a>

<p>A general-purpose register (one created or updated with the <code class="code">nr</code>
request; see see <a class="pxref" href="Registers.html">Registers</a>) is implicitly dimensionless, or reckoned
in basic units if interpreted in a measurement context.  But it is
convenient for many requests and escape sequences to infer a scaling
unit for an argument if none is specified.  An explicit scaling unit
(not after a closing parenthesis) can override an undesirable default.
Effectively, the default unit is suffixed to the expression if a scaling
unit is not already present.  GNU <code class="code">troff</code>&rsquo;s use of integer
arithmetic should also be kept in mind (see <a class="pxref" href="Numeric-Expressions.html">Numeric Expressions</a>).
</p>
<p>The <code class="code">ll</code> request interprets its argument in ems by default.
Consider several attempts to set a line length of 3.5&nbsp;inches when
the type size is 10&nbsp;points on a terminal device with a resolution
of 240 basic units and horizontal motion quantum of 24.  Some
expressions become zero; the request clamps them to that quantum.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ll 3.5i      \&quot; 3.5i (= 840u)
.ll 7/2       \&quot; 7u/2u -&gt; 3u -&gt; 3m -&gt; 0, clamped to 24u
.ll (7 / 2)u  \&quot; 7u/2u -&gt; as above
.ll 7/2i      \&quot; 7u/2i -&gt; 7u/480u -&gt; 0 -&gt; as above
.ll 7i/2      \&quot; 7i/2u -&gt; 1680u/2m -&gt; 1680u/24u -&gt; 35u
.ll 7i/2u     \&quot; 3.5i (= 840u)
</pre></div></div>

<a class="index-entry-id" id="index-measurements_002c-specifying-safely"></a>
<p>The safest way to specify measurements is to attach a scaling unit.  To
multiply or divide by a dimensionless quantity, use &lsquo;<samp class="samp">u</samp>&rsquo; as its
scaling unit.
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