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<title>Measurements (The GNU Troff Manual)</title>
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<div class="section-level-extent" id="Measurements">
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<p>
Next: <a href="Numeric-Expressions.html" accesskey="n" rel="next">Numeric Expressions</a>, Previous: <a href="Text.html" accesskey="p" rel="prev">Text</a>, Up: <a href="GNU-troff-Reference.html" accesskey="u" rel="up">GNU <code class="code">troff</code> Reference</a> [<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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<hr>
<h3 class="section" id="Measurements-1">5.3 Measurements</h3>
<a class="index-entry-id" id="index-measurements"></a>
<a class="index-entry-id" id="index-scaling-indicator"></a>
<a class="index-entry-id" id="index-indicator_002c-scaling"></a>
<a class="index-entry-id" id="index-units-of-measurement"></a>
<a class="index-entry-id" id="index-measurement-units"></a>
<p>The formatter sometimes requires the input of numeric parameters to
specify measurements. These are specified as integers or decimal
fractions with an optional <em class="dfn">scaling unit</em> suffixed. A scaling unit
is a letter that immediately follows the last digit of a number. Digits
after the decimal point are optional. Measurement expressions include
‘<samp class="samp">10.5p</samp>’, ‘<samp class="samp">11i</samp>’, and ‘<samp class="samp">3.c</samp>’.
</p>
<a class="index-entry-id" id="index-basic-units_002c-conversion-to"></a>
<a class="index-entry-id" id="index-units_002c-basic_002c-conversion-to"></a>
<a class="index-entry-id" id="index-conversion-to-basic-units"></a>
<p>Measurements are scaled by the scaling unit and stored internally (with
any fractional part discarded) in basic units.
<a class="index-entry-id" id="index-device-resolution_002c-obtaining-in-the-formatter"></a>
<a class="index-entry-id" id="index-resolution_002c-device_002c-obtaining-in-the-formatter"></a>
The device resolution can therefore be obtained by storing a value of
‘<samp class="samp">1i</samp>’ to a register. The only constraint on the basic unit is that
it is at least as small as any other unit.
</p>
<dl class="table">
<dd><a class="index-entry-id" id="index-basic-scaling-unit-_0028u_0029"></a>
<a class="index-entry-id" id="index-u-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-u"></a>
<a class="index-entry-id" id="index-scaling-unit-u"></a>
</dd>
<dt><code class="code">u</code></dt>
<dd><p>Basic unit.
</p>
</dd>
<dt id='index-inch-scaling-unit-_0028i_0029'><span><code class="code">i</code><a class="copiable-link" href='#index-inch-scaling-unit-_0028i_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-i-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-i"></a>
<a class="index-entry-id" id="index-scaling-unit-i"></a>
<p>Inch; defined as 2.54 centimeters.
</p>
</dd>
<dt id='index-centimeter-scaling-unit-_0028c_0029'><span><code class="code">c</code><a class="copiable-link" href='#index-centimeter-scaling-unit-_0028c_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-c-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-c"></a>
<a class="index-entry-id" id="index-scaling-unit-c"></a>
<p>Centimeter; a centimeter is about 0.3937 inches.
</p>
</dd>
<dt id='index-point-scaling-unit-_0028p_0029'><span><code class="code">p</code><a class="copiable-link" href='#index-point-scaling-unit-_0028p_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-p-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-p"></a>
<a class="index-entry-id" id="index-scaling-unit-p"></a>
<p>Point; a typesetter’s unit used for measuring type size.
There are 72 points to an inch.
</p>
</dd>
<dt id='index-pica-scaling-unit-_0028P_0029'><span><code class="code">P</code><a class="copiable-link" href='#index-pica-scaling-unit-_0028P_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-P-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-P"></a>
<a class="index-entry-id" id="index-scaling-unit-P"></a>
<p>Pica; another typesetter’s unit. There are 6 picas to an inch and
12 points to a pica.
</p>
</dd>
<dt><code class="code">s</code></dt>
<dt><code class="code">z</code></dt>
<dd><p>See <a class="xref" href="Using-Fractional-Type-Sizes.html">Using Fractional Type Sizes</a>, for a discussion of these units.
</p>
</dd>
<dt><code class="code">f</code></dt>
<dd><p>GNU <code class="code">troff</code> defines this unit to scale decimal fractions in the
interval [0, 1] to 16-bit unsigned integers. It multiplies a quantity
by 65,536. See <a class="xref" href="Colors.html">Colors</a>, for usage.
</p></dd>
</dl>
<p>The magnitudes of other scaling units depend on the text formatting
parameters in effect. These are useful when specifying measurements
that need to scale with the typeface or vertical spacing.
</p>
<dl class="table">
<dt id='index-em-scaling-unit-_0028m_0029'><span><code class="code">m</code><a class="copiable-link" href='#index-em-scaling-unit-_0028m_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-m-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-m"></a>
<a class="index-entry-id" id="index-scaling-unit-m"></a>
<p>Em; an em is equal to the current type size in points. It is named thus
because it is approximately the width of the letter ‘<samp class="samp">M</samp>’.
</p>
</dd>
<dt id='index-en-scaling-unit-_0028n_0029'><span><code class="code">n</code><a class="copiable-link" href='#index-en-scaling-unit-_0028n_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-n-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-n"></a>
<a class="index-entry-id" id="index-scaling-unit-n"></a>
<p>En; an en is one-half em.
</p>
</dd>
<dt id='index-vertical-space-unit-_0028v_0029'><span><code class="code">v</code><a class="copiable-link" href='#index-vertical-space-unit-_0028v_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-space_002c-vertical_002c-unit-_0028v_0029"></a>
<a class="index-entry-id" id="index-vee-scaling-unit-_0028v_0029"></a>
<a class="index-entry-id" id="index-v-scaling-unit"></a>
<a class="index-entry-id" id="index-unit_002c-scaling_002c-v"></a>
<a class="index-entry-id" id="index-scaling-unit-v"></a>
<p>Vee; recall <a class="ref" href="Page-Geometry.html">Page Geometry</a>.
</p>
</dd>
<dt id='index-M-scaling-unit'><span><code class="code">M</code><a class="copiable-link" href='#index-M-scaling-unit'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-unit_002c-scaling_002c-M"></a>
<a class="index-entry-id" id="index-scaling-unit-M"></a>
<p>Hundredth of an em.
</p></dd>
</dl>
<ul class="mini-toc">
<li><a href="Motion-Quanta.html" accesskey="1">Motion Quanta</a></li>
<li><a href="Default-Units.html" accesskey="2">Default Units</a></li>
</ul>
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