Motion Quanta (The GNU Troff Manual)

#### 5.3.1 Motion Quanta

An output device’s basic unit `u` is not necessarily its smallest addressable length; `u` can be smaller to avoid problems with integer roundoff. The minimum distances that a device can work with in the horizontal and vertical directions are termed its motion quanta. Measurements are rounded to applicable motion quanta. Half-quantum fractions round toward zero.

Register: `\n[.H]` ¶
Register: `\n[.V]` ¶

  These read-only registers interpolate the horizontal and vertical motion quanta, respectively, of the output device in basic units.

For example, we might draw short baseline rules on a terminal device as follows. See Drawing Geometric Objects.

    .tm \n[.H]
        error→ 24
    .nf
    \l'36u' 36u
    \l'37u' 37u
        ⇒ _ 36u
        ⇒ __ 37u