1919, 1¢ Green, Imperf Horizontally, vertical pair, light oval cancel, choice centering, rich vibrant color, Extremely Fine and choice, an exceptional example of the 1919 1¢ imperforate horizontally variety, grossly undercataloged in used condition; with 2007 P.F. certificate for block. Scott No. 538a  $150. To date, only 16 used sound pairs of this variety have been certified by the Philatelic Foundation. $0 (Image)