Calculate the Diff on your query and use the Diff column on your Form:
modify your query:
SELECT Nz(Stop_Current,0)-Nz(Current_Price,0) AS Diff, *
FROM (SELECT Investments01_tbl.Stock_Name, Investments01_tbl.Symbol_Stock, Investments01_tbl.Investmentl_ID, Investments01_tbl.Stop_Current...