Need Gadget to display the difference between the dates


We have the requirement to display difference between the dates in the graph format on the gadget. we have three custom fields

  1. Project Type with the values Project-A, Project-B, Project-C and Project-D.
  2. Sample Forecast Date
  3. Actual Submission Date

we need the gadget to display if we select the Project-A value then the corresponding difference between the dates of sample Forecast Date and Actual Submission Date. In the same way if we select Project-B etc.

Could you please help me anyone. Kindly let me know for any additional information.

Thanks in advance.