It would help to post your entire calculation expression.
If all possible values are numeric, you could simply choose the number return type and select the thousands separator option as part of the field's number format.
Is there a reason the calculation returns a Text type result? You can format number fields (incl. calculation fields with a Number result) to display as deciimal, with a thousands separator of your choice.
This is is my calculation
Case (Purchase Option Type 1= "Fair Market Value"; "FMV"; Lease No Trade PO 1)
where the field "Lease No Trade PO 1" is a number field. In order for the calculation to return
"FMV" if true then the result has to be text. Correct?
I do not need to use this result as a number (for calculation reasons) in any way, it will only be used for reporting reasons.
Yes, that is correct. But it seems like the purpose of this calculation is display - and this could be solved by placing both the text "FMV" and the field Lease No Trade PO 1 on the layout, and apply conditional formatting.