Pratishakhya ( '), also known as Parsada ('), are Vedic-era manuals devoted to the precise and consistent pronunciation of words. These works were critical to the preservation of the Vedic texts, as well as the accurate ritual recitations and analyses of the Vedas, particularly when isolated words interact after they have been joined in "sandhi" procedures. Each Vedic school ("parisad", or "parsad") and geographic branch ("sakha") developed their own manuals, explaining why they have come to be called "parsada" or "pratisakhya".