[NTG-context] [Widgets] Any good examples for developing JS-enabled PDFs that calculate?

Hi everyone, My goal is to have a PDF that - allows users to input numeric information in various fields, - makes calculations on the data in those fields, - ...and reports that information somewhere in the PDF. It seems that the widget support could handle this, but I'm struggling to understand how the pieces go together; does anyone have an example of this use case I could puzzle over? Many thanks! -Paul