Variables and expressions
=========================

Assign a value to a name and reuse it. Numeric values can drive dimensions
through expressions:

.. sheeptext::
   :alt: A box whose width comes from a variable expression

   scale = 2
   box width scale * 10

Because the width is computed, changing the variable changes every shape that
depends on it — one edit, many effects. Expressions support the usual
arithmetic, so you can express relationships between sizes rather than
hand-tuning each number:

.. sheeptext::
   :alt: Two boxes whose widths are derived from a shared base value

   base = 8
   A: box "narrow" width base * 6
   B: box "wide" width base * 12 at (0, 120)

Next: combine everything into a real diagram in :doc:`architecture`.