protected override void Calculate()
 {
     if (textBox_FromUnit.Text != string.Empty)
     {
         LengthConverter lenthConverter = new LengthConverter(decimal.Parse(textBox_FromUnit.Text),
                                                              comboBox_FromUnit.Text.Replace(" ", "_"),
                                                              comboBox_ToUnit.Text.Replace(" ", "_"));
         textBox_ToUnit.Text = lenthConverter.ConvertUnit().ToString();
     }
 }