Subtense bar is an instrument used for A. levelling B. measurement of horizontal distances in plane areas C. measurement of horizontal distances in undulated areas D. measurement of angles

levelling
measurement of horizontal distances in plane areas
measurement of horizontal distances in undulated areas
measurement of angles

The correct answer is: C. measurement of horizontal distances in undulated areas.

A subtense bar is a surveying instrument used to measure horizontal distances in undulated areas. It consists of a horizontal bar with two perpendicular sights at each end. The sights are used to align the bar with two points on the ground, and the distance between the points is then measured using a tape measure or other surveying instrument.

A subtense bar can be used to measure distances over long distances, and it is particularly useful for measuring distances in areas with a lot of hills or other obstacles. It is also a relatively inexpensive instrument, making it a popular choice for surveyors and other professionals who need to measure horizontal distances.

The other options are incorrect because:

  • A levelling instrument is used to measure the difference in elevation between two points.
  • A theodolite is an instrument used to measure angles.
  • A tape measure is a device used to measure distances.