Surveying Notes for GATE, PSU examinations -Part 1
(1) Principle of Surveying followed to prevent accumulation of errors is to work from whole to a part.
(2) Curvature of the earth's surface is taken into account only if the extent of survey is more than 260 sq. km
(3) A scale representing either three units or only one unit and its fractions up to second place of decimal point is Diagonal scale.
(4) The difference in the length of an arc and its subtended chord on earth's surface for a distance of 18.5 Km is 15 mm.
(5)Engineering survey is carried out to determine quantities and for collection of data for reservoirs.
(6) If smallest division of a vernier is longer than the smallest division of its primary scale, then vernier is called retrograde vernier.
(7) The smallest length that can be drawn on a map is 0.2 mm.
(8) A well conditioned triangle has angles not less than and more than respectively 90 and 120 degrees respectively.
(9) If n is value of one smallest division on main scale, v is value of one smallest division on the vernier and n is number of division on the vernier, then least count is given by s/n.
(10) Incorrect holding of chain at arrow is compensating error.
(11) French cross staff is used to set out 45 degrees offset with a chain.
(12) A discrepancy is the difference between two measured values of the same quantity.
(13) A chain 33 feet long and consisting of 16 links is a revenue chain.
(14) Every 20 m chain should be accurate to within +-5 mm.
(15) Methods used for chaining on the sloping ground are Stepping method and Hypotenusal allowance method.
(16) Compensating errors in chaining are proportional to the square root of the length of the line.
(17) Error due to bad ranging is cumulative positive.
(18) Negative errors are caused in chain, when its length is more than the standard length.
(19) An error under the same conditions always of the same size and sign, is called systematic and cumulative error.
(20) Errors which remain after mistakes and systematic errors have been eliminated are called Accidental errors.
(Ref: GATE 2013- GK Publishers.)