10¢ Plum 6UR8
"A line from the top to the fifth line above the bottom of the spandrel, the retouched line intersects 6 or 7 lines at the top"A Retouch of the Vertical Line in the Upper Left from the Top Line
Research notes:
Note the short horizontal line in the RNB, just to the right at the top of the '0'; this line is constant and will confirm the plate position.