//Button <<
        private void BtnPrevious_Click(object sender, RoutedEventArgs e)
        {
            double PreviousResult = Calculations.GiveBackPreviousElementOfResultMemory();

            double ExceptionValue = -9999.6677712;

            if (PreviousResult != ExceptionValue && PreviousResult != 0)
            {
                TbResultMemory.Text = PreviousResult.ToString();
                Calculations.DecrementResultMemoryNavigatorByOne();
            }
        }