Hi Yung Ming Lee,
I saw you Excel file along with your macro, and understand your requirement of creating an automated serial numbers, based on the user inputs.
I can clearly do the project for you, and moreover I will give an useful view of the sheet, which can be useful for any other analysis.
To be honest, I am good in Microsoft Office Package, along with the VBA. You can see my Excel Add-on, that I have created, in my portfolio.
I can finish this project in less than a day, hope so, if your objectives does not differ.
Thanks for the opportunity. You can contact me at any time.