In order to cancel the last input , select "Undo" item of menu. Then, the last entered control point disappears, and the menu item "Redo" is enabled. If you select "Redo" item, the disappeared control point will be recovered. Another way of undoing is to press key. For coordinates input, "Undo" and "Redo" can be repeated as many times as it is effective. For example, if you are creating a spline curve and have entered 5 control points so far, you can consecutively undo these 5 points by selecting repeatedly "Undo" item. At the moment all the points are undone, there is a beep sound indicating that there are no more points to undo.