private void DecimalInput(object sender, KeyPressEventArgs args)
        {
            const int BACKSPACE = 8;
            const int DECIMAL_POINT = 46;
            const int ZERO = 48;
            const int NINE = 57;
            const int NOT_FOUND = -1;

            int keyvalue = (int)args.KeyChar; // not really necessary to cast to int

            if ((keyvalue == BACKSPACE) ||
            ((keyvalue >= ZERO) && (keyvalue <= NINE)))
                return;
            // Allow the first (but only the first) decimal point
            if ((keyvalue == DECIMAL_POINT) &&
            ((sender as TextBox).Text.IndexOf(".") == NOT_FOUND))
                return;
            // Allow nothing else
            args.Handled = true;
        }