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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
\l'36u' 36u
\l'37u' 37u
    ⇒ _ 36u
    ⇒ __ 37u