Stamps perforated, horizontally and vertically, by differently gauged machines are sometimes said to be "perforated, compound of ... and ...". There are many difficulties in the way of obtaining a full knowledge of the combinations and vagaries of perforating-machines. PERFORATION-GAUGE.--A means of measuring PERFORATION or ROULETTE, which see. PHILATELIC.--The adjective of PHILATELY. PHILATELIST.--One who studies stamps. PHILATELY--from two Greek words, "φίλος" (= fond of) and "ἀτέλεια" (= exemption from tax)--signifies a fondness for things (_viz._, stamps) which denote an exemption from tax, _i.e._, that the tax, or postage, has been paid. The word is a little far-fetched to imply the _study_ of stamps, but as "Philately" has been the accepted term for over forty years, "Philately" it will doubtless remain, even if some one succeeds in finding a word which more accurately expresses the popular and scientific hobby. PIN-PERFORATED.--_See_ PERCÉ. PLATE is the term used, not always quite correctly, to describe the ultimate reproductions from the die which constitute the printing surface in the manufacture of stamps: the word covers not only a sheet of metal with stamps engraved on it, but also a group of CLICHÉS or a _forme_ of _printer's type_ and even a _lithographic_ stone. PLATE NUMBER is the consecutive number of each plate of a particular value, appearing on the margin of the plates and (in some of the British series) on the stamps themselves. POSTAL-FISCAL is a fiscal stamp the use of which for postal purposes has been duly authorised, in contradistinction to a "fiscal postally used," a use which has been tacitly permitted in many countries. POSTAL STATIONERY, _i.e._, envelopes, postcards, letter-cards, wrappers, telegram forms, &c.: frequently termed ENTIRES. POSTMARK.--The official obliteration applied to a stamp to prevent its further postal use. PRE-CANCELLED.--Two or three countries have adopted the system, to save time in the post-office, of supplying sheets of stamps cancelled prior to use. This may be a convenience, but the practice undoubtedly opens the door to possible fraud. PRINT is an impression taken from any die, plate, forme, or stone.