Sub Demo()
With ActiveSheet.UsedRange.Rows
C = Application.Match("PFOS*", .Item(1), 0)
If IsError(C) Then Beep: Exit Sub
Application.ScreenUpdating = False
For R& = 3 To .Count
With .Cells(R, C)
If .Value < 0.1 And .Value >= 0.001 Then .NumberFormat = "0." & String$(3 - (.Value < 0.01), "0")
End With
Next
Application.ScreenUpdating = True
End With
End Sub