Math
====

Small numeric helpers in ``richy.core.math``. The module is
intentionally tiny -- it's a parking lot for one-off calculations
shared across apps.

calc_percentage_change
----------------------

Returns the percentage change from a starting value to an ending
value as a ``float``. Used everywhere a "% change" is rendered --
performance charts, share-price percentage columns, drawdown, etc.

.. autofunction:: richy.core.math.calc_percentage_change