About GUI: I would delegate clear-cell and delete-row somewhere closer to the table, not in a menu (what if user wants to do lots of clearning-deleting?), and move load-save-spreadsheet to standard top-menu. Then, the button to the right of the textbox would no longer be needed.

And, '+' button could switch to 'open lens cover to scan' screen which would save the trouble of clicking the button yet-again after opening lens cover (it should be possible to catch lens-cover-being-opened event and hence start scanning). Optionally, lens-cover-being-closed could switch back to spreadsheet.

Thank you. Best wishes.