Hi Sparrow,
You have excellent eye-sight to spot the ',' instead of '.'! 
Derek.

This is only in glasses )))))))) And they still need to be found ))))
But seriously, these periods and commas like to present surprises in our regional standards.

There is no error in the calculated field.
I have a different decimal separator. There is indeed a difference.

He can use:

procedure FormMain_TableGridInvoices_OnChange (Sender: TObject);
begin
  TNxNumberColumn(FormMain.TableGridInvoices.Columns[9]).FormatMask := '#,##0.00';
end;

And I think you can do without printf in the calculated field.