Leveling Flashcards
a. Instrument out of adjustment
b. Rod not of standard length
c. Defective rod
Instrumental errors
Bubble not centered
b. Parallax
c. Faulty rod readings
d. Rod not held plumb
e. Incorrect setting of target
f. Unequal backsight and foresight distances
Personal errors
Curvature of the earth
b. Atmospheric refraction
c. Temperature variations
d. Wind
e. Settlement of the instrument
Natural errors
a fixed point of reference whose elevation is either known or assumed.
Bench mark (BM)
a reading taken on a rod held on a point of known or assumed elevation.
Backsight (BS)
a reading taken on a rod held on a point whose elevation is to be determined.
Foresight (FS)
measured from the center of the instrument to the rod on which a backsight is taken.
Backsight distance
the horizontal distance from the center of the instrument to the rod on
which a foresight is taken.
Foresight distance
an intervening point between two bench marks upon which point
foresight and backsight rod readings are taken to enable a leveling operation to continue from a new instrument position.
Turning point (TP)
the elevation of the line of sight of an instrument above or below a selected reference datum.
Height of instrument or height of collimation (HI)
curved line which graphically portrays the intersection of a vertical plane with the
surface of the earth.
Profile
numerical designation given in terms of horizontal distance any point along a
profile line is away from the starting point.
Stationing
taken along the centerline of the proposed project to provide an accurate representation of the ground surface.
Intermediate foresights or ground readings
points which are established along the profile level route at uniformly measured
distances.
Full stations
any other intermediate point established along a profike level route which is not designated as a full station.
Plus stations
