HOROLOGION - The Horologion ( Chasoslov, ), or Book of Hours, provides the Acolouthia of the Daily Cycle of services  as used by the Orthodox and Eastern Catholic Churches. Into this fixed framework, numerous moveable parts of the services are inserted.

The Horologion is primarily a book for the use of the Reader and Cantor as distinguished from the Euchologion, which contains the texts used by the Priest and Deacon.