horizontal pair used alongside pair of 1906 2c Red & black with overprint reading up (21), normal 1906 2c Red & black (23), and 1909 2c Vermilion & black (27), all tied by Ancon cancels to locally-addressed November 9, 1909 registered cover, left stamp of the error pair with small scuff, cover with vertical filefold and slightly reduced at left, the only example of this error on cover and one of the great rarities of the Canal Zone, an exhibit-quality item which has been missing from very nearly every collection, 2005 Philatelic Foundation certificate (Scott $2,000 for used)