Noun
perforation gauge (plural perforation gauges)
(philately) A device for measuring the number of perforations per 2 centimetre distance along the edge of a postage stamp.
Tools Philately uses a number of tools, including stamp tongs (a specialized form of tweezers) to safely handle the stamps, a strong magnifying glass and a perforation gauge (odontometer) to measure the perforation gauge of the stamp. Source: Internet