2 1/2 s. greenly, ON BOTH SIDES VERTICAL DOUBLE PERFORATION, by which on the left with part of the next stamp, when correctly stamped single franking on invoice cover with K1 " ST.P.A. Hamburg 6/12 (1865) " Copenhagen/Denmark (arrival postmark). The condition is perfect certificate Lange BPP small perforation damage " below, otherwise. Double perforations are known to almost all perforated stamps. On cover however of a very big rareness. Interesting document ".