The masonry instruments, which vary in size from a few feet to 90 feet in height, are Jai Singh's chief work.G.R. Kaye, The Astronomical Observatories of Jai Singh
When Jai Singh designed the observatories, one of his foremost objectives was to create astronomical instruments that would be more accurate and permanent than the brass instruments in use at the time. His solution was to make them large, really large, and to make them of stone and masonry. This simple yet remarkable decision brought forth a collection of large scale structures for the measurement of celestial movement that is unequalled today. Among the many startling impressions for a visitor to one of the observatories, is the scale of the instruments. One is literally enveloped, and confronted with a space that is both aesthetic and mathematical. The time scale of the Samrat Yantra at Jaipur, for example, includes subdivisions as fine as two seconds, and as one watches, the motion of the gnomon’s shadow becomes a palpable experience of earth’s cosmic motion.