Which instrument's accuracy specification is given as 5 mm + 5 ppm in the distance example?

• A. Theodolite
• B. GNSS Receiver
• C. Level
• D. The electronic total station

Answer: (D)

The main idea is how distance measurements are specified for devices that actually measure distance, not just angles or positions. An accuracy expressed as 5 mm + 5 ppm means there is a fixed error of 5 millimeters plus an additional error that grows with the distance at a rate of 5 parts per million. This form is typical for electronic distance measuring (EDM) components found in a total station, where both a constant bias and a scale error with distance influence the result. The instrument that combines EDM with angle measurements and is used for distance to prism targets is the electronic total station, so this 5 mm + 5 ppm specification aligns with its distance measurement capability. The other instruments don’t use this distance-error model: a theodolite measures angles, a GNSS receiver provides position fixes with different error characteristics not expressed in this mm-plus-ppm form, and a level determines height differences with its own leveling-error metrics.