Works dealing with the calculation of time. These include calendars, Easter Tables, almanacs, and other astronomical / astrological texts , as well as specific treatises such as the Venerable Bede's De temporum ratione of 725. Manuscripts of computus texts often include diagrams and even figural decoration. See also Vade mecum and volvelle.
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Michelle Brown. Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).