The world's first postage stamps, issued by Great Britain in 1840, were without means of
self-separation. They are called "imperforate" or, abbreviated, "imperf." Such stamps had
to be cut apart...
Stamps in sheets are stacked in quantity and the comb is punched through the top row. Then
the comb is moved to the next row and so on. The comb does not always line up exactly with
the preceding row...