The correct answer is D. Theodolite is an instrument used for measurement of both horizontal and vertical angles.
A theodolite is an optical instrument that measures both horizontal and vertical angles. It is used in a wide variety of surveying applications, including construction, engineering, and land surveying. Theodolites are typically mounted on a tripod and have a telescope that can be rotated to view objects in the distance. The angle between the telescope and the horizontal is measured using a circular scale called a horizontal circle. The angle between the telescope and the vertical is measured using a circular scale called a vertical circle. Theodolites can also be equipped with electronic distance measurement (EDM) devices, which allow them to measure the distance to objects in the distance.
Option A is incorrect because theodolites are not used to tighten the capstan-headed nuts of level tubes. The capstan-headed nuts of level tubes are tightened using a wrench.
Option B is incorrect because theodolites can be used to measure vertical angles as well as horizontal angles.
Option C is incorrect because theodolites can be used to measure both horizontal and vertical angles.