What is height of instrument and Rise & fall method of levelling?

Question

I want to what is height of instrument and Rise & fall method of levelling? What is the method to calculate reduced level.

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Answer ( 1 )

  1. Height of Instrument (HI) method: consider the readings taken in the operation shown below:

    Reduce level can be computed using the following expression:

    RL of a point = HI – FS = ( RLBM +BS) – FS

    Arithmetic check: ΣBS – ΣFS= Last RL – first R

    Where:

    RL: Reduce Level

    HI: height of instrument

    FS: foresight

    BS: Back sight

    BM: Bench Marks

     

    Rise and fall (RF) method: the rise or fall of the ground between successive rod stations is considered. For the same instrument set up,

    If 2nd rod reading > first rod reading ⇒ fall

    If 2nd rod reading < first rod reading ⇒ rise

    Then RL of 2nd station = RL of first station – fall       or

    RL of first station + rise

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