The name is derived from Yantra, instrument, and Mantra, for formula or, in this context, calculation. Therefore jantar mantar means literally calculation instrument. Jantar Mantar is colloquially equated with the magical practices where "Mantar" refers to the incantation (or spell) and Jantar Mantar refers to questionable magical arts (astrology falling into such arts).The yantras have evocative names like, samrat yantra, jai prakash, ram yantra and niyati chakra; each of which are used to for various astronomical calculations.The primary purpose of the observatory was to compile astronomical tables, and to predict the times and movements of the sun, moon and planets.