Variables in Scheduled Transactions?

[Robert Uhl]

How does one use variables in scheduled transactions?  I cannot seem to
find anything in the docs except for tantalising references...

Ideally, I'd like to have a variable which decrements each month, in
order to automatically calculate sum-of-digits depreciation.

-- 
Robert Uhl <http://public.xdi.org/=ruhl>
I would rather be exposed to the inconveniences attending too much
liberty than those attending too small a degree of it.
                                   --Thomas Jefferson