Using Fixed Units to update remaining duration

I am having difficulty working with resource dependent activities; specifically, I have a project-specific series of tasks for which I have some reliable production data and I thought it might be helpful to reconsider activity durations in terms of what we've seen from the contractor to date v. what they programmed into the schedule (durations not supported by any resource, estimate, etc).

My thought was to change the activity type from Task to Resource dependent, the duration from Fixed Duration/Units/Time and Fixed Units, and apply a new resource (material) that represents the number of "widgets" associated with the activity and impose a production limit using the resource Max Units/Time field.  My hope was that I could manually input budgeted units (# of widgets) and the program would calculate the "required duration" automatically.  Nothing happens however.

Anyone have any advice?  I've been racking my brain over this all weekend.

Thanks!