How to create Custom-Functions within our Custom Addins?

May consider this: 

1. Create a VBA Add-In:

• • Open Excel and press Alt + F11 to open the VBA Editor.
  • Go to Insert > Module to create a new module.
  • Write your custom function in VBA:

Function MultiplyByTwo(num As Double) As Double
    MultiplyByTwo = num * 2
End Function

• • Save your file as an Add-in:
    • Go to File > Save As.
    • Choose Excel Add-In (*.xlam) as the file type.

2. Install the Add-In:

• • Go back to Excel.
  • Open File > Options > Add-Ins.
  • At the bottom, select Excel Add-ins and click Go.
  • Click Browse and select your saved .xlam file.
  • Once added, your custom functions will be available for use in any workbook by typing =MultiplyByTwo().

3. Create a Ribbon Tab for Custom Functions:

• • • Use the Office Ribbon Editor (a free third-party tool) or build the Ribbon XML yourself using VBA or .NET.
    • Customize your ribbon to include a tab (e.g., "Anupam_Tools") and assign buttons to your custom functions.