What is referred to when discussing any object of known length used in surveying?

In surveying, the term that is best associated with an object of known length is primarily the reference rod. A reference rod is a precise and calibrated rod used by surveyors to establish a specific length or to provide a point of reference in their measurements. This instrument allows surveyors to ensure accuracy in their work when measuring distances and heights.

Using a reference rod is essential in surveying practices, as it helps provide a reliable benchmark or standard for comparison to other measurements. Their usage ensures that surveyors can achieve consistent and accurate results, which are critical in the field.

While a Jacobs staff is also used in surveying, primarily serving as a vertical measurement tool, it does not specifically denote an object of known length in the same sense as a reference rod does. Likewise, distance measures and calibration standards refer to broader concepts or tools used in surveying but do not focus on an object that has the primary purpose of being a known length for reference.