About Lesson
Booking methods, their reduction and arithmetic checks
There are two primary ways to book and reduce level observations:
- Rise and Fall Method
- This method calculates the difference in elevation between two consecutive points by comparing their staff readings. The difference between the back sight (BS) and the fore sight (FS) indicates the rise or fall:
- Rise occurs when the back sight reading is greater than the fore sight.
- Fall occurs when the fore sight is greater than the back sight.
- The Reduced Level (RL) of each point is calculated by adding the rise or subtracting the fall from the RL of the preceding point.
- Height of Instrument (Collimation) Method
- In this method, the height of the instrument (H.I.) is determined for each instrument setup by adding the back sight (BS) to the elevation of the benchmark (BM).
- The reduced level (RL) of the first station is obtained by subtracting the fore sight (FS) from the instrument height (H.I.).
- For subsequent setups, the H.I. is recalculated by adding the back sight (BS) of the current station to the RL of the preceding point.
- The reduced level of the last station is obtained by subtracting its fore sight from the current instrument height.