What plotting command are you running? I thought the tick marks pointed in ***by default***. They do in my IDL 6.4 and others. In any case, the control for direction is in the graphics keyword [X|Y|Z]TICKLEN, which, when set to a positive value, makes the tickmarks point inside the plot bounding box, and, when set negative, makes thes point away from the bounding box.
James Jones
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