Reference Sheet in Add-In not Active Workbook

[vb2themax]

I have an add-in that has a formula that uses a named range on one of it's sheets to lookup values needed to complete the calculation. My question is how do I in the formula located in the Add-in reference the sheet in the Add-in and not the ActiveWorkbook:

Snippet of my code in the add-in:
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' Location for Exact Mass data
Set wsSheet = ThisWorkbook.Sheets("Mass_Table")
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need this to be something like:
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' Location for Exact Mass data
Set wsSheet = ThisAddIn.Sheets("Mass_Table")
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I would like to use this calculation in other sheets but each time I do, it will not work because there is no "Mass_Table" sheet in the workbook I am trying to user the UDF in, it is located in the Add-in only.

Hope this makes sense. Any help would be appreciated.