INSTRUMENT USE FOR SETTING OUT THE RIGHT ANGLE

INSTRUMENT USE FOR SETTING OUT THE RIGHT ANGLE

During the survey for setting out right angle (90°) following instrument are

used.

1. Cross-staff

2. Optical Square

3. Prism square

4. Site square

1. Cross staff - It is classified in 3 types-

A. Open cross staff (O.C.S)

B. French cross staff(F.C.S)

C. Adjustable cross staff (A.C.S)

A. Open cross staff - It's only measured 90° Angle

B. French cross staff - It's measured 45°

, 90°and 135° angle

C. Adjustable cross staff - It measured 0°

 to 360°all anlge

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2. Optical Square- It measured only right anle (90°) or in optical square their are

two prism those are at horizontal and they both are at 45° Angle.

3. Prism square - It's working principle is same as optical square but the basic

difference is its reflecting angle is not adjustable.(The prism square has same principle as that of optical square but it is more modern or accurate instrument. It has the merit that no adjustable or adjustment is required since the angle between reflecting surface.)

4. Site square- Site square is the type of instrument that connect 2 telescope

those are in horizontal and are in the angle of 90°