Which tool is commonly referred to as a Jacob's staff in surveying?

The tool commonly referred to as a Jacob's staff in surveying is indeed a leveling rod. This tool is essential for establishing accurate height differentials and determining elevations during leveling surveys. A Jacob's staff typically features a graduated scale that allows surveyors to read measurements easily and precisely.

In the context of surveying, the leveling rod is used in conjunction with a spirit level or a theodolite for sighting and transferring heights. The design enables surveyors to align their line of sight with the instrument, facilitating accurate leveling across a distance.

For clarity, while measuring tape, vertical interval tools, and reference staffs serve specific purposes within surveying, they do not carry the designation of Jacob's staff. Measuring tapes are primarily used for distance measurements, vertical interval tools help in assessing elevation gains over a specific distance, and reference staffs serve as markers for maintaining a baseline height. None of these fulfill the critical role of height determination in the same way as a leveling rod.