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Q: Which one of the following instruments is better and accurate in measurement of right angles?
  • A. Open cross staff
  • B. Adjustable cross staff
  • C. French cross staff
  • D. Optical square
Correct Answer: Option D - Optical square–Optical square is somewhat more convenient and accurate instrument than the cross staff for setting out a line at right angles to another line. Cross staff–The simplest instrument used for setting out right angle is a cross staff. The common forms of cross staff are– 1. Open cross staff 2. French cross staff 3. Adjustable cross staff.
D. Optical square–Optical square is somewhat more convenient and accurate instrument than the cross staff for setting out a line at right angles to another line. Cross staff–The simplest instrument used for setting out right angle is a cross staff. The common forms of cross staff are– 1. Open cross staff 2. French cross staff 3. Adjustable cross staff.

Explanations:

Optical square–Optical square is somewhat more convenient and accurate instrument than the cross staff for setting out a line at right angles to another line. Cross staff–The simplest instrument used for setting out right angle is a cross staff. The common forms of cross staff are– 1. Open cross staff 2. French cross staff 3. Adjustable cross staff.