Dhanur-yantra

 was an instrument used by early Indian astronomers.

It was one of Lalla's 12 instruments of astronomy.

It is essentially half of a cakra-yantra (i.e. it's a half-circle). It can help to measure nāḍis elapsed, and the degrees above the horizon of the Sun.

Ãryabhaṭa says it is used in conjunction with a flat circle on the ground and a gnomon shadow to calculate elapsed ghaṭīs in the day.

Lalla describes a modification to it, called a Kartarī-yantra.