The present invention is a system that positions an interface for a pen-based computer at an end of a natural user motion arc, such as an arc a hand travels when an elbow is pivoted. Positioning of the interface in a lower corner of a display or window (left corner for a right-handed person and right corner for a left-handed person) allows easy approach when the user is working in the center of the display, such as when drawing on the pen-based computer display. An arc or curved interface improves approach zones and reduces unintended selections of controls or buttons within the interface. The arc allows the natural motion to be extended by wrist or finger motions to access all the controls in the corner command interface. Controls on the arc are placed to allow any underlying pop-up menus to be completely accessible when an activated. Overflow menu items of activated controls of the interface are located in conformity to the natural arc.