« Back to Dictionary Index

Back Observation (Back Sight)

A back observation, also known as a back sight, refers to a specific type of observation or measurement made using instruments from a previously occupied station point.

Definition and Purpose:

  • Definition: A back observation is an instrumental measurement taken at a surveying or observational station that has just been vacated. It involves using instruments, such as a theodolite or transit, to measure angles, distances, or heights from the current station back to a previously occupied station.
  • Instrumental Use: This technique is commonly employed in surveying, astronomy, and other scientific disciplines where precise measurements from fixed points are required.

Key Characteristics:

  • Procedure: After completing measurements or observations at one station (the forward station), the observer moves to the next station and sets up instruments to make a back observation towards the previous station (the back station).
  • Verification: Back observations serve to verify or cross-check measurements, ensuring accuracy and consistency in surveying or observational data.


  • Surveying: In land surveying, a back sight is crucial for establishing precise alignments, verifying angles, and ensuring that measurements are made correctly from one point to another.
  • Astronomy: Astronomers use similar techniques to establish fixed points in the sky relative to Earth’s position, aiding in celestial navigation and mapping.


  • Accuracy: By taking back observations, surveyors and scientists can reduce errors and uncertainties in measurements, enhancing the reliability of data collected.
  • Verification: Provides a means to validate the consistency and reliability of measurements made from different vantage points or stations.

A back observation, or back sight, is an essential practice in surveying and observational sciences where precise measurements and alignments are critical. It involves using instruments to measure from a current station point back to a previously occupied station, ensuring accuracy, verification, and consistency in surveying data and scientific observations. This technique plays a fundamental role in maintaining the integrity and reliability of spatial and observational measurements across various disciplines.

« Back to Dictionary Index