Theodolite and telescope definitions clarify instrument types and applicable standards for angle and distance measurement. A telescope is an instrument that collects and focuses electromagnetic radiation to magnify distant objects, with optical and radio variants; a theodolite is a portable surveying instrument comprising a sighting tube or telescope and horizontal and vertical graduated circles for measuring angles. Vernier theodolites have movable vernier scales in sliding contact with graduated circles; they are less precise than advanced optical designs but are used widely for small and large scale surveys due to lower cost and simplicity, and separate specifications address different theodolite types.