//Validate Depth Values using Keypress
 private void textBox3_KeyPress(object sender, KeyPressEventArgs e)
 {
     if (Char.IsControl(e.KeyChar) == false && Char.IsDigit(e.KeyChar) == false)
     {
         MessageBox.Show("Please enter a number");
         e.Handled            = true;
         DepthField.BackColor = Color.Red;
         DepthField.Focus();
     }
     else
     {
         DepthField.BackColor = System.Drawing.SystemColors.Window;
     }
 }
        //Validate Depth Values using Constraint

        private void textBox3_Validating(object sender, CancelEventArgs e)
        {
            if (int.TryParse(DepthField.Text, out int DepthInput) == true)
            {
                if (DepthInput < Desk.MINDEPTH || DepthInput > Desk.MAXDEPTH)
                {
                    MessageBox.Show("Please enter a depth from " + Desk.MINDEPTH + " to " + Desk.MAXDEPTH + " inches");
                    DepthField.Text      = String.Empty;
                    DepthField.BackColor = Color.Red;
                    DepthField.Focus();
                }
                else
                {
                    DepthField.BackColor = System.Drawing.SystemColors.Window;
                }
            }
        }