Actually this is incorrect. Move to the Left [Backspace] or Right [Spacebar] depending on which margin you wish to change until it beeps. You hold down [ALT] and press [3] M REL, then move left or right again until you get where you want, then Hold [ALT] and press either [4] L MAR or [5] R MAR.
As a side note the Manual for this Typewriter IS available at Brother's website at http://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_SX4000_EN_219.PDF
Hope this helps!
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