The observer lays down in the hemishere and focuses on the stars through a sighting tube, whose end is held by the metal ring. The elongation of the tube onto the sphere's inside surface shows a star's position by reading the coordinate lines. To simplify measurement the Jai Praksh Yantra is made of two hemispheres, themselves complementary. In place of the passages in one hemisphere threre are marble scales of the other and vice versa. Alternating use of the hemispheres within a two hours change allows observation around the clock.
One can walk on the inside of the hemispheres.
In the bottom left-hand corner the centre of the scale that is half visible in the big picture.