What is a theodolite and how does it work?

A theodolite is a precision instrument for measuring horizontal and vertical angles. It consists of a telescope mounted on graduated circles for angle measurement. The instrument is leveled using bubble levels, centered over a station using plumb bob or optical plummet, and angles are read from vernier or micrometer scales. Types include vernier theodolite (reads to 20 seconds), micrometer theodolite, and digital/electronic theodolite. Used for traversing, triangulation, and setting out works.