1918, 1¢ Gray Green, Offset, Imperf Between, horizontal pair, face-free wavy line machine cancel, natural s.e. at right as always, bold color, Fine and attractive, the Unique Used Example of the 1918 1¢ Offset Imperforate Vertically Between Variety, grossly undervalued in the Scott catalog; with 2004 P.F. certificate. Scott No. 525c  $650 for the grade of fine. Due to the nature of this error, all examples except one have the perforations cutting into the left stamp in the pair and all have a natural straight edge on the right side. In total, only seven pairs have been certified as genuine by the Philatelic Foundation. This example being the unique used pair. $0 (Image)