Q3. What are cylinder numbers?

Cylinder Number: The practice of inscribing the plate or cylinder number on the sheets of a printing of definitive stamps has greatly widened the horizon of philatelic research and the study of the deifinitive stamps. This help the collector to follow the printing history of an issue and make note of any change in the stamp design, size, paper, watermark, perforation types, gum and flaws, retouches etc, in the consecutive printings and record them accurately in a chronological order, in terms of cylinder numbers and pane identification.