Where to find a VBA function's source in Excel
I hope I understand your question... From reading other answers I see that it is not a recorded macro. It's safe to assume then that someone wrote it in VBA. Try the following:
- Press Alt+F11 to open your VBA editor
- Click View -> Project Explorer (it may already be visible.) (or: CTRL+R)
- You should see "VBAProject(your workbook name.xls). Click that.
- Click one of the sheets under 'Microsoft Excel Objects' in the Project explorer.
- Click View -> Code
- Click Edit -> Find
- Type the name of the function in the box
- Ensure 'Current Project' is selected.
- Click Find Next
That should take you to where the function is written.
Press ALT + F11 to see the VBA project window. You should be able to find the code for the custom function in there.
Microsoft has written a documenation for VBA. It is sorted for objects, not for functions, but if you don't need to type an object's name before the function, it is likely to be a function of an object you are currently working with, like the current workbook. This documentation can be read here. http://msdn.microsoft.com/en-us/library/bb149081.aspx Try looking for the function in objects like Workbook, Sheet, etc., and if it isn't there, use the search option on the site (warning: this search used to be bad, now it seems to be a bing search, so maybe it is better now). You won't be able to see the source for the function, but there is a comprehensive API there.
If you cannot find the function there and think that it is not a standard Excel function, there is the question of where did Excel get it from in order to execute it. Try debugging a macro calling the function in question, and use the "step into button". If you see the source, you've solved your problem. If it isn't there, it may come from an external application communicating with Excel. Go to the Button "Office", there choose Excel options, there go to Add-Ins. You can look at the addins installed and hunt down their documentation.
If all else fails and/or is too cumbersome, you can always google something like "[name of function] + Excel + VBA +Documentation]". Maybe you'll find some online documentation.