gistfile1.vb

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim rango_a_calcular As Range
    
    Set rango_a_calcular = Range("D3:F12")
    
    If Not Application.Intersect(rango_a_calcular, Range(Target.Address)) Is Nothing Then
        For i = 1 To rango_a_calcular.Rows.Count
            Dim fila_actual As Integer
            Dim medida_2 As Integer
            Dim medida_3 As Integer
            Dim medida_4 As Integer
            
            fila_actual = rango_a_calcular.Rows(i).Row
            medida_2 = Cells(fila_actual, 4).Value
            medida_3 = Cells(fila_actual, 5).Value
            medida_4 = Cells(fila_actual, 6).Value

            Cells(fila_actual, 8 ).Value = (medida_2 + medida_3 + medida_4) / 3
        Next
    End If
End Sub