private void rbResidential_CheckedChanged(object sender, EventArgs e)
{
// When Residential radio button is checked
// We disable the second KWH entry box and ask the user to enter regular KWH
// Change the labels
lblKWH1.Text = "Enter kWh Used:";
lblKWH2.Text = "";
// Clear the two KWH entry boxes
txtKWH1.Text = "";
txtKWH2.Text = "";
// Set the tags for the KWH entry boxes
txtKWH1.Tag = "Enter kWh Used";
txtKWH2.Tag = "";
// Enable the first entry box, but disable the second one
txtKWH1.ReadOnly = false;
txtKWH2.ReadOnly = true;
// Provide the Residential description in the rich text box
rtbCustDesc.Text = Residential.CustomerDescription();
}