Surveying instruments are used to measure and map the Earth's surface. The most common instruments used in surveying are the alidade, ylevel, TRANSIT, handlevel, and THEODOLITE. An alidade is a device used to measure angles in surveying and astronomy. A ylevel is a surveying instrument used to measure the difference in elevation between two points. A TRANSIT is an instrument used to measure horizontal and vertical angles. A handlevel is a surveying instrument used to measure the difference in elevation between two points. Lastly, a THEODOLITE is an instrument used to measure both horizontal and vertical angles.