Hero's Dioptra

The "dioptra" devised by Hero is a portable surveying instrument for making accurate geodetic measurements. It measures azimuths, heights, lengths and angular distances.
The apparatus, which was mounted on a tripod about 50 cm tall, pivoted on a circular plate and was moved around horizontally by a worm screw driven by a small handle. The top plate was mounted on a toothed semicircular plate and was adjusted in the vertical plane by another worm drive. Angles could be read off the top disc, which was scored with two lines crossing at right angles. The sighting and reading elements were made of bronze.