Option Explicit

Private sinFTime(1 To 2) As Single, sinETime(1 To 2) As Single
Private Sh As Worksheet

Sub ScreenUpdating2()
    Dim i As Long, ii As Long
        Set Sh = Worksheets(2)
        Sh.Cells.ClearContents
        For i = 17 To 26
            Worksheets(1).Activate
            Call TestC
            Worksheets(2).Activate
            Cells(1, 1).Activate
            Call TestD
            For ii = 1 To 2
                Worksheets(1).Cells(i, ii + 1).Value = sinETime(ii)
            Next
        Next
End Sub

Private Sub TestC()
    Dim i As Long, j As Long, k As Long
    sinFTime(1) = Timer
    For i = 1 To 10
        For j = 1 To 30
            For k = 1 To 20
                Sh.Cells(j, k).Value = i
            Next
        Next
        Sh.Cells.ClearContents
    Next
    sinETime(1) = Timer - sinFTime(1)
End Sub

Private Sub TestD()
    Dim i As Long, j As Long, k As Long
    sinFTime(2) = Timer
    For i = 1 To 10
        For j = 101 To 130
            For k = 1 To 20
                Sh.Cells(j, k).Value = i
            Next
        Next
        Sh.Cells.ClearContents
    Next
    sinETime(2) = Timer - sinFTime(2)
End Sub