backsight

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backsight

[′bak‚sīt]
(engineering)
A sight on a previously established survey point or line.
Reading a leveling rod in its unchanged position after moving the leveling instrument to a different location.
(navigation)
A marine sextant observation of a celestial body made by facing 180° from the azimuth of the body and using the visible horizon in the direction in which the observer is facing.

backsight

In surveying, a sight on a previously established survey point or line.
References in periodicals archive ?
In common practice, a backsight would be recorded from the benchmark and the target would be set for the desired elevation of the forms.
The backsight reading is added to the elevation of the existing benchmark to establish the height of the line-of-sight, reference line.
A backsight is recorded for the benchmark, and a foresight is recorded for the turning point.
The rod readings are recorded in the columns labeled BS, backsight, and FS, foresight.
If the instrument height is not changed, the backsight for the closure will be the same rod reading as the foresight used to determine the elevation of benchmark two.
The backsight on station A is not a problem, but the foresight to station B contacts the ground before reaching station B.
The first rod reading is a backsight on station A (see Figure 5-19).
19 feet) is recorded in the station A row of the backsight column and is used to determine the height of the instrument (108.
Each time the instrument is moved, it must be leveled and a backsight recorded to reestablish the height of the instrument (see Figure 5-21).
97 feet is recorded in the TP1 row of the backsight column and is added to the elevation of TP1, 101.