When you Save a computed point in a COGO dialog, TPC saves the information needed to undo the save and displays an Undo button in the dialog. When you choose Undo, one of two things happens:
1) If the Save created a new point, TPC removes the new point from the survey. If you have choosen to plot this point or it created a point that was automatically plotted in the current drawing, you will see the point disappear from the drawing. If you have the Points Manager open, you will also notice that the point is removed from the Points Manager. Infact, the created point is removed from all dialogs, views and drawings in the survey. It's completely gone.
2) If the Save updated an existing point, TPC restores the original point data for that point and redraws and redisplays that point in any views, dialogs or drawings and use it.
In either case, after the point has been undone, the Undo button dissappears and is not displayed until you again Save a computed point in that dialog.
You can close and re-open a dialog that displays the Undo button and still execute the Undo.
COGO Commands - reference