at the back of Yantra Raj, There is another instrument called Dakshinobhitti Yantra.
It is a big wall, placed in north to south line of meridian. The east face of the
instrument is inscribed with two quadrants of 20 feet radius and on the west face a semi
circle of 19 feet 10 inches radius. The arcs are mainly constructed of white marble and
graduated in degrees as well as minutes. To have an accuracy in measuring the
calculations, and minute readings, the steps are arranged so that one can reach very close
to the graduation. At the center of the quadrants and semi-circle, short pegs are fixed.
The instrument is mainly used for observing the different altitude of heavenly bodies.
Fixing the thread on one of
the center pegs, the observer moves the other end of the thread over the graduations,
until the thread is exactly alinged on the object to be observed. The reading from the
upper end of the arc gives altitude.
By observing the shadow every
day, the maximum and minimum zenith distance of the sun can be known. Half of this
difference, is the maximum declination or obliquity of the ecliptic. At the time of noon
the sun is on the meridian and the shadow of the peg falls on the graduations, the
reading is taken from the positions of the shadow.