Line perforation is made by a machine which punches a single row of holes at a time. First, it makes horizontally than vertically. The two line of holes do not match perfectly at each corner of the stamps. In comb perforation the' lines of perforation are made in both directions at the same time. Comb perforation gives a neater appearance at the corner of the stamps.
Perforations vary from stamp to stamp.
These are measured by the number of holes in a space of two centimeters. Perf.12' means 12 holes in 2 cm. Perf.12 x 13 means that the perforation at top and bottom is 12 and the perforation at sides is 13. There exist some special gauges to measure the perforations. Perforation gauges are sold with instructions for their use and it requires only a little practice.