ELIZABETHAN NAVIGATIONAL CLOCK COMPENDIUM3D Model
At the most general level, a compendium is simply an instrument made up of several disparate elements. An astronomical compendium is a mathematical instrument which has a range of astronomical functions incorporated into a single small device.
As a catch-all term there is no standard list of functional elements, but sundials, compasses, calendars, maps, astrolabes, quadrants and various tables are often to be found. Neither is there a standard form for the resulting instrument; astronomical compendia are found in many shapes and formats, whether rectangular, circular, oval or octagonal, and are sometimes constructed to mimic other artefacts, such as books, with covers and leaves.
Astronomical compendia seem to have been particularly favoured in the 16th century