There is no country that is collected in a more specialized way than are the stamps of Austria. Most specialists of other countries seek cancels and covers and blocks and all kinds of specialty items. But Austrian specialists go far further. Austrian specialty catalogs list paper varieties along with varieties listed by thickness as measured by a micrometer. Machine made and hand made paper types of the first issues are listed (the only country that I know of that does this) as are various ribbing and laid papers. Throughout, the philately of Austria is a obsessive-compulsives dream.
This degree of Austrian specialization is part of the tradition of Austrian collecting. Beginning in the early part of the Twentieth Century, Edwin Mueller began issuing a series of specialized catalogs that proved to be most detailed in the world. This tradition has been carried on by Ulrich Ferchanbauer, who is the current King of Austrian philately, having issued a specialized catalog several years ago that is a masterpiece of specialization. The stamp pictured above, which has a Ferchenbauer certificate, is a Scott #2. Ferchanbauer lists this stamp, to which Scott gives a single number, in thirteen major types. Each country has its own specialty quotient, the degree to which its collectors pursue minutia. Austria seems to be at the top of the OCD list.