leaky integrators and sine waves

[from Jeff Vancouver 990125.1512 EST]

I have a couple of questions for the modelers, particularly the Vensim
modelers. I am trying to operationalize a sine wave to disturb a level
variable. In other words, I am trying to get an environmental variable to
exhibit waves like Rick gets in his demos. Second, I am trying to
operationalize what I think you people call a leaky integrator (again, in
Vensim). The issue is that the controller is not given calibration
information so that over time, I would expect calibration to float about a
bit, probably in a single direction.

Whenever I ask a question I have no idea whether someone is going to
immediately understand what I am asking or whether it makes not sense. If
you know something about Vensim or leaky integrators, but do not understand
my question, I would appreciate if you asked for clarification. My quess
is that at least a couple of you know the answers I seek, but we may need
to put some heads together.