Hi,
This is not a bug. Or at least it was meant for it to work this way.
The initial value for the variable is not part of the series.
That initial value is used by the engine to display instead of null,
before the calculations begin.
If you want the -15 to be subtracted, you should make the
Unfortunately the documentation is a little thin on this subject. In
fact the documentation would lead one to believe that using the
initial value expression would do exactly what Justin expected (from
the online tutorial):
variable name=QuantitySum class=java.lang.Double
