demonstrating knowledge of basic geometry. The inhabitants of Indus civilisation also tried to standardise measurement of length to a high degree of accuracy. They designed a ruler—the Mohenjo-daro ruler—whose unit of length (approximately 1.32 inches or 3.4 centimetres) was divided into ten equal parts. Bricks manufactured in ancient Mohenjo-daro often had dimensions that were integral multiples of this unit of length. Mehrgarh, a Neolithic IVC site, provides the earliest known evidence for in vivo drilling of human teeth, with recovered samples dated to 7000-5500 BCE. Early astronomy in India—like in other cultures— was intertwined with religion. The first textual mention of astronomical concepts comes from the Vedas—religious literature of India. According to Sarma (2008): "One finds in the Rigveda intelligent speculations about the genesis of the universe from nonexistence, the configuration of the universe, the spherical self-supporting earth, and the year of 360 days divided into 12 equal parts of 30 days each with a periodical intercalary month." Classical Indian astronomy documented in literature spans the Maurya (Vedanga Jyotisha, c. 5th century BCE) to the Vijaynagara(South India) (such as the 16th century Kerala school) periods. The first named authors writing treatises on astronomy emerge from the 5th century, the date when the classical period of Indian astronomy can be said to begin. Besides the theories of Aryabhata in the Aryabhatiya and the lost Arya-siddhānta, we find the Pancha-Siddhāntika of Varahamihira. The astronomy and the astrology of ancient India (Jyotisha) is based upon sidereal calculations, although a tropical system was also used in a few cases. Alchemy (Rasaśāstra in Sanskrit)was popular in India. It was the Indian alchemist and philosopher Kanada who introduced the concept of 'anu' which he defined as the matter which cannot be subdivided. This is analogous to the concept of atom in modern science. Linguistics (along with phonology, morphology, etc.) first arose among Indian grammarians studying the Sanskrit language. Aacharya Hemachandrasuri wrote grammars of Sanskrit and Prakrit, poetry, prosody, lexicons, texts on science and logic and many branches of Indian philosophy. The Siddha-Hema-Śabdanuśāśana includes six Prakrit languages: the "standard" Prakrit(virtually Maharashtri Prakrit), Shauraseni, Magahi, Paiśācī, the otherwise-unattested Cūlikāpaiśācī and Apabhraṃśa (virtually Gurjar Apabhraṃśa, prevalent in the area of Gujarat and Rajasthan at that time and the precursor of Gujarati language). He gave a detailed grammar of Apabhraṃśa and also illustrated it with the folk literature of the time for better understanding. It is the only known Apabhraṃśa