The 'differential levelling' method gives heights by:
Choose the correct answer
Measuring horizontal distances only
RL of new point = RL_known + backsight − foresight; arithmetic check: Σ(BS)−Σ(FS) = last RL − first RL
Angular observations with theodolite
GPS satellite ranging only
Correct Answer
B. RL of new point = RL_known + backsight − foresight; arithmetic check: Σ(BS)−Σ(FS) = last RL − first RL
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Differential levelling: measures height difference between points by observing backsight (BS) and foresight (FS) readings on a levelling staff with a level instrument. RL of point = RL_known + BS − FS. Arithmetic check: Σ(BS) − Σ(FS) = Last RL − First RL. Closing error distributed proportionally (Bowditch). Series of instrument setups needed for long distances.
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