Unnatamsa is an instrument for measuring Altitude of an object in the sky.
The large graduated brass circle hung from the supporting beam, is the measuring instrument of the Unnatamsa. The brass circle is pivoted to rotate freely around a vertical axis. The ring has two cross beams in the vertical and horizontal directions. A sighting tube is pivoted at the centre of the circle, which can be moved in the vertical direction, to align towards any celestial object.
The vertical movement of the sighting tube and the horizontal rotation of the brass ring are adjusted to sight the celestial object.
The rim of the brass circle has graduations marked in such a way that smallest division is a tenth of a degree. The larger divisions of 1 degree and of 6 degrees are also marked on the circle. After sighting the celestial object, its Altitude can be read from the position of the pointer of the sighting tube against the graduations on the rim of the circle.