pdmode is a "point" resolution setting for lack of a better definition. If you go to your format pulldown, and go to point style, you will see the "graphics" for points. 3 is just an 'X' on screen. 0 is the period/dot, 1 is "nothing", literally nothing, you cant select it, other #'s generate different pics. Anyway, pick a graphic, and type pdmode and you will see the corresponding number