Tidal wheel from BL Harley 3017, f. 135

Tidal wheel showing the thirty-day lunar cycle in correspondence with the tides, with the earth at the centre of the diagram and four circles in the outer corners representing the four moons. Image taken from f. 135 of A Carolingian miscellany of computational and astronomical texts and tables, including decennovenal (19-year) cycles (ff. 3v-8) a calendar (ff. 22-32v), formulae (ff. 42v-50, 60-65, 66), Egyptian days (ff. 58v-60), Greek and runic alphabets (f. 61), and 'Revelatio Esdrae' (ff. 63-64v). Written in Latin and Greek.

The "BL Harley Manuscript" refers to a collection of medieval manuscripts held in the British Library in London. The Harley Manuscripts are part of the larger collection known as the Harley Collection, which was assembled by Robert Harley (1661–1724) and his son Edward Harley (1689–1741). Robert Harley was a prominent English statesman and bibliophile, and he began amassing a vast collection of books and manuscripts in the late 17th and early 18th centuries.

The Harley Manuscripts are known for their diversity and include a wide range of texts, including historical chronicles, illuminated manuscripts, legal documents, literary works, and scientific treatises. The collection contains over 7,000 manuscripts, and it is considered one of the most important manuscript collections in the British Library.

The Harley Manuscripts are numbered with the prefix "Harley," followed by a specific manuscript number. Each manuscript in the collection has its own unique content and history, and they cover a broad spectrum of topics and time periods. Some of the manuscripts in the collection are beautifully illuminated, with intricate illustrations and decorations.