The length of the ruling edge should be equal to the smaller side of the plane table. A plane alidade can be used only when the elevations of the of the objects are low. PLANE ALIDADE. SPRIT LEVEL- THE MAGNETIC COMPASS A box compass consists of a magnetic needle pivoted at its centre freely. It is used for orienting the plane table to magnetic north. The edges of the box compass are straight and the bottom is perfectly flat. PLUMBING FORK The plumbing fork consists of a hair pin-shaped brass frame, having two equal arms. One end has a pointer while a plumb bob is attached the other end. It is used in large scale survey for accurate centering of the station location on the table over its ground position. It is also used for transferring the location of the instrument station on the sheet on to the ground. The fork is placed with its upper arm lying on the top of the table and the lower arm below it. The table is said to be centered when the plumb bob hangs freely over ground mark.
The length of the ruling edge should be equal to the smaller side of the plane table. A plane alidade can be used only when the elevations of the of the objects are low. PLANE ALIDADE. SPRIT LEVEL- THE MAGNETIC COMPASS A box compass consists of a magnetic needle pivoted at its centre freely. It is used for orienting the plane table to magnetic north. The edges of the box compass are straight and the bottom is perfectly flat. PLUMBING FORK The plumbing fork consists of a hair pin-shaped brass frame, having two equal arms. One end has a pointer while a plumb bob is attached the other end. It is used in large scale survey for accurate centering of the station location on the table over its ground position. It is also used for transferring the location of the instrument station on the sheet on to the ground. The fork is placed with its upper arm lying on the top of the table and the lower arm below it. The table is said to be centered when the plumb bob hangs freely over ground mark.
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