Automatic Level, Digital Level and Optical Theodolites
11.1 Automatic Level
The automatic level employs a gravity-referenced prism or mirror compensator to orient the line of sight (line of collimation) automatically. The instrument is quickly levelled when a circular spirit level is used. When the bubble has been centered (or nearly so), the compensator takes over and maintains a horizontal line of sight, even if the telescope is slightly tilted (see Fig. 11.1).
Automatic levels are extremely popular in present-day surveying operations and are available from most of the survey instrument manufacturers (Fig. 11.2). They are easy ...