Of great importance for the understanding of the sacrificial ceremonial are the Prayogas ("Manuals") and Paddhatis ("Guides"), of which a vast number exist in manuscript. These works represent both the Çrauta and the Grihya ritual according to the various schools. The Prayogas describe the course of each sacrifice and the functions of the different groups of priests, solely from the point of view of practical performance, while the Paddhatis rather follow the systematic accounts of the Sutras and sketch their contents. There are also versified accounts of the ritual called Karikas, which are directly attached to Sutras or to Paddhatis. The oldest of them appears to be the Karika of Kumarila (c. 700 A.D.). Of a supplementary character are also the class of writings called Anukramanis or Vedic Indices, which give lists of the hymns, the authors, the metres, and the deities in the order in which they occur in the various Samhitas. To the Rigveda belonged seven of these works, all attributed to Çaunaka, and composed in the mixture of the çloka and trishtubh metre, which is also found in Çaunaka's Rigveda Pratiçakhya. There is also a General Index or Sarvanukramani which is attributed to Katyayana, and epitomises in the Sutra style the contents of the metrical indices. Of the metrical indices five have been preserved. The Arshanukramani, containing rather less than 300 çlokas, gives a list of the Rishis or authors of the Rigveda. Its present text represents a modernised form of that which was known to the commentator Shadguruçishya in the twelfth century. The Chhandonukramani, which is of almost exactly the same length, enumerates the metres in which the hymns of the Rigveda are composed. It also states for each book the number of verses in each metre as well as the aggregate in all metres. The Anuvakanukramani is a short index containing only about forty verses. It states the initial words of each of the eighty-five anuvakas or lessons into which the Rigveda is divided, and the number of hymns contained in these anuvakas. It further states that the Rigveda contains 1017 hymns (or 1025 according to the Vashkala recension), 10,580-1/2 verses, 153,826 words, 432,000 syllables, besides some other statistical details. The number of verses given does not exactly tally with various calculations that have recently been made, but the differences are only slight, and may be due to the way in which certain repeated verses were counted by the author of the index.