The theodolite in which the telescope can be revolved through a complete revolution in a vertical plane is called ______.

Explanation:

Transit Theodolites:

(i) Earlier the theodolites were manufactured with long telescopes which could not be rotated through 180° about the horizontal axis i.e. in the vertical plane.

(ii) Later on theodolite with shorter telescopes were developed which could be rotated through 180° in the vertical plane about the horizontal axis. These theodolites are called as transit theodolites since in them; the line of sight can be rotated about the horizontal axis.

(iii) Now a days, all the theodolite are manufactured with small telescope, and thus the words theodolite and transit theodolite are used synonymously.

Additional Information

Theodolites are of two types

(i) Vernier theodolite: The least count of vernier theodolite is 20 second (20")

(ii) Optical Theodolite: The least count of optical theodolite is 1 second (1")