PS Traverse & Leveling Calculations 3

Question 1

In differential leveling, a backsight (BS) of 8.42 ft is taken on BM-A with elevation 312.65 ft. What is the Height of Instrument (HI)?

Accepted Answer

321.07 ft

Answer

HI = Elevation of BM + BS reading = 312.65 + 8.42 = 321.07 ft.

Question 2

With an HI of 321.07 ft and a foresight (FS) of 5.63 ft on TP-1, what is the elevation of TP-1?

Accepted Answer

315.44 ft

Answer

Elevation of TP-1 = HI − FS = 321.07 − 5.63 = 315.44 ft.

Question 3

What arithmetic check verifies differential leveling notes for a closed loop returning to the starting benchmark?

Accepted Answer

ΣBS − ΣFS should equal zero

Answer

For a closed leveling loop, ΣBS − ΣFS = 0 confirms arithmetic; for an open line it equals the net elevation change.

Question 4

Three-wire leveling improves precision by:

Accepted Answer

Reading top, middle, and bottom stadia crosshairs to average the rod reading and detect errors

Answer

Three-wire leveling reads all three horizontal crosshairs; the mean of the top and bottom wires should match the center wire, providing a check.

Question 5

Reciprocal leveling is primarily used to:

Accepted Answer

Carry elevations across wide obstacles such as rivers where a balanced setup is impossible

Answer

Reciprocal leveling makes setups on both sides of an obstacle and averages results, largely canceling curvature and refraction errors.

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