Difference between fixed hair and movable hair of tachometry..

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Sr.no	Fixed hair	Movable hair
1	In this method interval between two stadia hair is fixed.	In this method interval between two stadia hair is variable. Stadia line are not fixed and moved by micrometre screw.
2	In this method horizontal distance from the instrument to the staff can be determine from the value of staff intercept intercepted by the stadia line.	In this method horizontal distance from the instrument to the staff can be determine from the value of stadia variable interval.
3	Staff intercept varies with the distance at which the staff is held.	The staff is provided with two vanes or target fixed at a known distance apart normally 3m to staff.
4	This method is commonly used	This method is not commonly used but now rarely used.

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