Traverse & Leveling Calculations Flashcards

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)?

Answer: 321.07 ft

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

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?

Answer: 315.44 ft

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

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

Answer: ΣBS − ΣFS should equal zero

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

Three-wire leveling improves precision by:

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

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

Reciprocal leveling is primarily used to:

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

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

The combined effect of Earth curvature and atmospheric refraction on a sight distance of 1 mile is approximately:

Answer: 0.57 ft

Combined curvature and refraction correction ≈ 0.574 M² ft (M in miles), giving about 0.57 ft at 1 mile.

In profile leveling, intermediate foresights (IFS) differ from turning-point foresights (FS) in that:

Answer: IFS readings yield ground elevations but do not establish a new HI — the instrument is not moved

An intermediate foresight is a minus-sight only (Elev = HI − IFS); no turning point is established, so the HI remains unchanged.