NumberFormat in cells with if function

Please, i cant solve this

Sub Format_Cell_Hektari()
If Cells(1, 1) = "ha" Then Cells(1, 2).NumberFormat = "#,##0.0000" ' ...( if Cells(1,1) not equal to "ha" then stay "#,##0.00")
End Sub

but i wont this macro always active in this sheet

ps. sory my english is not so good