Great job! If you do any more work on it, I would like to see the feature already suggested of sending the result into SU measurement input field. Additionally, I'd really appreciate:
2) Non-modal (can switch back-and-forth) without forcing close);
3) Re-sizable (can reduce size without cropping);
4) Copy results
5) History of last {3 to 9} calculations.

However, if you do no more, you can rest on your laurels IMhO.