The Cosmographia of Petrus Apianus was one of the most popular books on cosmography ever published. One of the reasons its enormous popularity was the book's inclusion of ingenious paper devices called volvelles that enabled one to solve practical mathematical problems relating to time telling, the calendar, astronomy and astrology. This amazing paper instrument is entirely complete and original in all respects, including the original strings used as radial indicators. Apianus referred to this instrument as "Ptolemy's Instrument." It is used to tell the time of sunrise and sunset, length of day and time in any latitude. For the latter reason it is known as a "universal" instrument.

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