Which of the following methods of a tachometric survey is also known as the subtense method?

Explanation

Moveable hair method 

Stadia hair is not fixed but can be moved by means of micrometer screws.

•  The stadia hair can be moved in case of Movable hair method which is also known as subtense method.
• The intercept on leveling staff is kept constant and stadia hair interval is variable.
• The stall is provided with 2 vanes or targets fixed at a known distance apart.
• The variable stadia distance measured from this value, the required horizontal distance may be found out.
• It is a slow method as compared to other methods.

Additional Information 

Fixed hair method

• In this method distance between hairs is fixed
• If the stadia wires are fixed, this method is known as Fixed hair method.
• The intercept on leveling staff is variable and the stadia hair interval is fixed.
• The staff intercept value varies with its distance from the instrument, this is most commonly used in tacheometry  

Tangential hair method

• In the tangential hair method, the stadia hairs are not used.
• The readings being taken against horizontal crosshair.
• It is slower than the stadia hair method.