How to Create an Add-In Macro

To save a workbook as an Add-In, choose Save As... from the File menu. Choose Microsoft Excel Add-In from the Save File As Type drop-down list box, then press OK. In Excel for Windows, Add-In macros are automatically given the filename extension. xla. 

Your custom functions will now be indistinguishable from Excel s built-in functions. By giving them names using lower-case letters, you can distinguish them from Excel s built-in functions. 

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