Once you've rebuilt the add-in (F7 in VS 6 or Shift+Ctrl+B in VS.NET or VS 2005), you can test it in Excel as shown below.
Notice that the function returns an informative error string if the Prices argument is not well-formed.
Notice also how #NUM! is returned if the calculation fails (in this case because of a zero price) even though the data is well-formed.
