This document provides information about tacheometry, which is a method of surveying that determines horizontal and vertical distances from instrumental observations. It discusses how tacheometry can be used when obstacles make traditional surveying difficult. The key aspects covered include: - Defining tacheometry and the measurements it provides - When tacheometry is advantageous over other surveying methods - The instruments used, including tacheometers and levelling rods - How horizontal and vertical distances are calculated using constants - The different types of tacheometer diaphragms and telescopes - The fixed hair method for taking readings