The Indian Astrolabe for sailors called ''Yantraraja'' developed during Sultanate and Mogul periods

 Indian maritime history is as old as 3,000 BC coinciding with the Indus Valley Civilisation, It is said 500-6000 years ago the Indus River was used for navigation purpose.  more than 5-6000 years ago. Harappans at Lothal in around 2,400 BC built  the world’s first dock, Amazing fact is its location - far away from high low tide activities  to avoid accumulation of silt nearby. This dock  has    berth facilities and service ships.  Modern oceanographers believe that Harappans had a better expertise in sea  tides, hydrography and maritime engineering,

Centuries ago, there was maritime trade activity  with the Mesopotamian Civilisation, apart  records are available  suggesting  Indian merchants had trade contacts initially in the nearby countries  and later  Far East and Arabia.  There is certain evidence of a ‘Naval Department’ existing during the Mauryan period.

Man's quest for exploring sea routes to find new lands across the globe over a period of  time increased manifold and exploring new countries gave then a chance to exchange ideas,  commodities, exports and imports, This international trade transaction  initially was based on barter system. With the advent of better tools and navigational  gadgets to sail high seas  transportation through oceans between countries got a boost. It further promoted mixing of people of different cultures and skills. 

It took hundreds of years  to develop various skills to move the heavy ships across the oceans so navigational skills evolved slowly, so was the instrumentation. Initially the sailors were dependent on the celestial maps - position of important stars in the sky, knowledge of climate, monsoon activities, tides and currents. 

Daring adventurers  navigated the ships in the dangerous high seas to reach lands unknown and far away. They purposely chose unknown Territories  by was of taking different risky sea routes not tried before.   Explorers like Vasco Da Gama, Ferdinand Magellan, Christopher Columbus, et al are worthy of mention  who successfully charted  new territories unknown to Europe in the pre-modern history.

The astrolabe is a two-dimensional depiction of the heavens whose layout is achieved using the mathematical technique of stereographic projection. The astrolabe was likely invented in Ancient Greece around 225 BCE and was based on the research of Hipparchus. 
Over 2,000 years ago, one or more  Astrolabe, a calculator that was capable of solving astronomical problems  became invaluable to astronomers, so was the maritime Astrolabe to mariners as well.
While traditional Astrolabes, also  known as planispheric astrolabes, calculated the altitude of celestial bodies, the maritime astrolabe was used to determine latitude. Being able to determine latitude was essential to helping mariners know where they were in a featureless ocean or sea

But the device  astrolabe  was refined in the Middle East over the course of several centuries, and eventually the Arabic astrolabe was reintroduced into medieval Europe in the 12th century. Travelling Iranian scholars introduced Islamic Astrolabes  into South Asia, particular India.  The Tughluq Sultans (1320–1410) in Delhi and the Mughal Emperors started making Astrolabes.

Jaipur Hindu astrolabe,

Large Hindu astrolabe

Above image:  Large Hindu astrolabe. Full view, graduated matt black perspex background. photo credit: © The Board of Trustees of the Science ..........

Large Hindu astrolabe collection

Above image: Large Hindu astrolabe. Detail of script on the top of astrolabe, graduated grey background. Science Museum Group Collection. photo credit: © The Board of Trustees of the Science ..........
Armed with better knowledge of maritime science, shipping building and basic climate and weather patterns, in the 14th century  an ingenious discovery of a new gadget was made. 
Astrolabe is called the ‘Yantraraja’  and in Sanskrit, it translates to the 'king of instruments'.  Now on display in the Geneva Museum of Science, this instrument was used to navigate the ship in the high-seas and is of Indo-Moroccan origin with Sanskrit inscriptions.  Made by Sivalala, this large astrolabe with Sanskrit script was commissioned by Raja Ramasimha in 1870 and the instrument was laid out for the latitude of Bundi (25º 28'), Rajasthan.

Iranian scholars introduced Astrolabes  into South Asia  The Tughluq Sultans (1320–1410) in Delhi and the Mughal Emperors started making Astrolabes.   The Islamic world preserved the Greek sci-ence of the astrolabe, as it did the other areas of Greek learning, elaborated upon it and disseminated it westwards and eastwards.Again, we do not have any definite information when the astrolabe was introduced into India. Al-B¯ır¯un¯ı, who wrote extensively on the astrolabe,may have introduced it to his Hindu interlocutors in north-western India inthe first quarter of the eleventh century. There are stray references to Mus-lim scholars, who migrated from Central Asia in the subsequent centuries,employing the astrolabe for astronomical and astrological purposes in Delhi.Definite evidence is available from the fourteenth century onwards. Con-temporary chronicles report that Sult.¯an F¯ır¯uz Sh¯ah Tughluq (r.1351-1388)got several astrolabes manufactured at Delhi and sponsored the composition of manuals on the astrolabe both in Persian and in Sanskrit .In the seventeenth, numerous astrolabes were produced in India with Arabic/Persian legends. These are generally classified as Indo-Persian astrolabes.

The very first Sanskrit manual on the astrolabe was composed in 1370 by a Jain monk called Mahendra S¯uri, who was a leading astronomer at the court of Firuz Shah at Delhi. This work, entitled
 Yantraraja. These Sanskrit manuals on the astrolabe must naturally have been accompanied by the production of Sanskrit astrolabes are in private collection in India and the USA.

The astrolabe was also patronised by Hindu rulers notably Maharaja Jai Singh II of Jaipur (1688–1743) (present day Rajasthan). During his reign (1699–1743),  and later by Sawai Singh (18th CE), Jaipur became a prominent centre for the production for astrolabes. Thr ru;rr's  flair for  astronomy led him to the construction of five astronomical observatories in Jaipur, Delhi, Mathura, Ujjain and Benares (now Varanasi).  The silver astrolabe (gifted to the Prince of Wales) has a tubular eyepiece commonly seen in astrolabes produced in Jaipur. They are  used to measure the position of stars and planets.