Which of the following statements are true about surveying instruments ? Select the correct answer from the codes given below :
(a) Indian Clinometer is used for measuring the height of relatively distant objects.
(b) Trough Compass is also used for plane table orientation.
(c) Prismatic Compass is used for reading fore and back bearing.
Codes :

Question

Which of the following statements are true about surveying instruments ? Select the correct answer from the codes given below : 
(a) Indian Clinometer is used for measuring the height of relatively distant objects. 
(b) Trough Compass is also used for plane table orientation. 
(c) Prismatic Compass is used for reading fore and back bearing.
Codes :

Accepted Answer

Option 1 is correct because all the statements (a), (b), and (c) are true regarding surveying instruments. Let's break down why:

*   **(a) Indian Clinometer is used for measuring the height of relatively distant objects:** This statement is true. An Indian Clinometer is a simple surveying instrument specifically designed to measure angles of elevation and depression. These angles, along with a known distance to the object, allow for the calculation of the object's height, especially when the object is relatively far away.

*   **(b) Trough Compass is also used for plane table orientation:** This statement is also true. A trough compass (also known as a box compass) is a rectangular compass often used in conjunction with a plane table. It helps in orienting the plane table to magnetic north, which is a crucial step in plane table surveying. By aligning the compass needle with the north mark, the plane table can be accurately oriented.

*   **(c) Prismatic Compass is used for reading fore and back bearing:** This statement is true as well. A prismatic compass is designed to measure bearings of lines. It allows the surveyor to directly read the bearing (the angle a line makes with magnetic north) through the prism. Fore bearing is the bearing of a line in the forward direction, and back bearing is the bearing of the same line in the opposite direction. The prismatic compass is well-suited for measuring both.

Now, let's explain why the other options are incorrect, keeping in mind that we must support Option 1 as the *only* correct answer:

*   **Option 2 (a and b):** This is incorrect because statement (c) is also true. The prismatic compass *is* used for reading fore and back bearings, making this option incomplete.

*   **Option 3 (a and c):** This is incorrect because statement (b) is also true. The trough compass *is* used for plane table orientation, making this option incomplete.

*   **Option 4 (b and c):** This is incorrect because statement (a) is also true. The Indian Clinometer *is* used for measuring the height of relatively distant objects, making this option incomplete.

Therefore, since all three statements (a), (b), and (c) are factually correct descriptions of the uses of these surveying instruments, Option 1 is the only correct answer.