• Theodolites or transits are used to measure horizontal angles. These have evolved as follows:
  • Vernier theodolite (open face and Vernier equipped instruments)
  • Optical theodolite (enclosed with optical readouts with direct digital readouts or micrometer equipped readouts)
  • Electronic theodolites (enclosed with electronic readouts)
• Electronic theodolites operate like any optical theodolite with one major difference that these instruments have only one motion (upper) and hence have only one horizontal clamp and slow motion screws.

• Angle least count can be 1" with precision ranging from 0.5" to 20"
• Digital readouts eliminate the personal error associated with reading and interpolation of scale and micrometer settings.
• Display window/unit for horizontal and vertical angles available at either one or both ends.
• Some digital theodolites have modular arrangement where they can be upgraded to be a total station or have an EDMI attached for distance measurements.
• Vertical circles can be set to zero for horizon or zenith along with the status of battery shown in the display window.
• Typical specifications for digital theodolites are generally given as follows:
  • Magnification: 26X to 30X
  • Field of view (FOV) 1.5⁰.
  • Shortest viewing distance 1.0 m
  • Angle readouts, direct 5" to 20"
  • Level sensitivity: plate level vial 40"/2 mm, circular level vial 10"/2 mm

The following description provides specifications for Nikon electronic theodolite (NE-202/203):

• Digital angle display is user-switchable from 5"/10" to 1"/5"
• Built-in vertical axis compensator automatically compensates for instrument inclination within ± 3' (NE-203)
• Accuracy is 5" in 5" display mode.
• Large, dot-matrix dual-line LCD screen displays both vertical and horizontal angles simultaneously.
• LCD screen and keyboard are placed on both sides of the alidade for easier operation
• Telescope magnification of 30X with a 45 mm objective aperture diameter.
• Employs a unique linear focusing mechanism to simplify focusing at both short and long distances. Minimum focusing distance of 0.7 m.
• Repeat horizontal angle measurement possible up to ±1999°59'55"
• Continuous operation for up to 48 hours with fresh alkaline-manganese batteries (NE-202)