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What is the meaning of a signal ‘Left arm extended’ given by a surveyor?
Continue to move towards your left
Plumb the rod towards your left
Move considerably towards your left
Move slowly towards your left
Continue to move towards your left
In surveying, the signal 'left arm extended' indicates that the ranging rod is not in the correct line and the assistant must shift the rod towards the left. This signal is used to guide the assistant to align the rod with the true survey line established by the surveyor.
IS 1491:1959 (Code of practice for setting out of buildings)
In surveying, the signal 'left arm extended' indicates that the ranging rod is not in the correct line and the assistant must shift the rod towards the left. This signal is used to guide the assistant to align the rod with the true survey line established by the surveyor.
Δx=xactual−xtarget — The lateral displacement required to reach the target line
The surveyor observes the rod from a fixed station. If the rod appears to the right of the correct alignment, the surveyor extends their left arm to communicate the direction in which the assistant needs to move. This visual feedback loop continues until the rod is exactly aligned, at which point the 'both arms extended' or 'both arms above head' signal is given to indicate the rod is fixed.
Surveying signals are vital for long-distance communication between the surveyor and the chainman.
Left arm extended signifies a requirement for lateral movement of the ranging rod towards the left.
Signals are standardized to prevent ambiguity in field operations.
The precision of ranging depends on the clarity of these signals and the response time of the field assistant.
Enables rapid communication over large distances without noise interference.
Reduces errors in manual alignment during chain surveying.
Reliance on clear visibility between the surveyor and the assistant.
Subject to human error if hand signals are not distinct.
Chain surveying for alignment of survey lines.
Setting out of civil engineering works and foundations.
Quick arm movement indicates a larger distance shift, whereas slow movement indicates a small correction.
Option B is incorrect as plumbing the rod refers to making it vertical, which is a different signal ('both arms above head, then brought down').
Option C and D relate to the speed of movement rather than the specific direction command defined by the standard signal convention.
A is correct — The signal 'left arm extended' is the standardized instruction for the assistant to continue moving the ranging rod towards their left to achieve the correct alignment.
Always remember that in surveying hand signals, the extended arm always points in the direction the rod needs to move to align with the surveyor's line of sight.
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