Private Sub CommandButton1_Click()
Dim plage As Range
Application.ScreenUpdating = False
On Error Resume Next
Set plage = Range("A1", Cells(Rows.Count, 1).End(xlUp))
With plage.Offset(, 255)
.FormulaR1C1 = "=-LEFT(RC1)"
plage.Font.Bold = False
Intersect(plage, .SpecialCells(xlCellTypeFormulas, 16).EntireRow).Font.Bold = True
.ClearContents
End With
End Sub