|Excel Developer Reference|
expression A variable that represents a CellFormat object.
This property returns True if the formula will be hidden when the worksheet is protected, Null if the specified range contains some cells withFormulaHidden equal to True and some cells with FormulaHidden equal to False.
Don’t confuse this property with the Hidden property. The formula will not be hidden if the workbook is protected and the worksheet is not, but only if the worksheet is protected.