The Margin Distance option is only active when the Margin Warning option is set to Enabled. You set the distance from the right margin of the dtterm window at which you want the bell to ring (or appear, if Bell Type is set to Visible). The default value is 10 characters.
To change the distance:
If the Global Options dialog box is not displayed, choose Global from the Options menu.
Click inside the Margin Distance text field in the Bell Control area and type the number of characters from the right margin of the window at which you want the margin warning to be issued.
Click OK at the bottom of the Global Options dialog box or press Return to save your selection and exit the window.
To save your selection and retain the window, click Apply.