9015.20 - Theodolites and tachymeters (tacheometers):

This HTS subheading covers theodolites and tachymeters, which are precision surveying instruments. Theodolites are primarily used for measuring horizontal and vertical angles, forming the fundamental basis for most land surveying operations. Tachymeters, also known as tacheometers, are more advanced instruments that combine the functions of a theodolite with a built-in distance measuring device (such as a telemeter or EDM), allowing for simultaneous measurement of angles and distances. These instruments are essential for creating maps, establishing boundaries, and conducting topographic surveys.

Distinguishing this category from its siblings, rangefinders (9015.10) are solely for determining distances, while levels (9015.30) are specifically designed for establishing a horizontal plane to measure height differences. Photogrammetrical surveying instruments (9015.40) utilize photography to create measurements and maps from aerial or terrestrial images, a different methodology than direct optical measurement. Other instruments and appliances (9015.80) encompass a broader range of surveying and measuring devices not specifically covered elsewhere in the 9015 heading.

Theodolites and tachymeters are further subdivided into electrical and non-electrical (other) categories. Electrical versions often incorporate digital displays, data logging capabilities, and integration with electronic distance measurement technology. The distinction is based on whether the instrument relies on electrical power and components for its primary function and measurement outputs.