When the staff reading increases between two consecutive points, the difference is recorded in which column in the Rise and Fall method?
Correct Answer: C. Fall
📚 Detailed Explanation: Increasing Staff Reading → Recorded in Fall Column
Why C (Fall column) is correct: In the Rise and Fall method, the relationship between consecutive staff readings determines whether the ground has risen or fallen. If the staff reading increases (next reading > previous), it means the ground dropped — because a higher reading means the staff base is lower relative to the horizontal line of sight.
Rise and Fall Method: Decision Rule
| Comparison | Difference | Column to Record In | Meaning |
|---|---|---|---|
| Previous reading < Current reading (INCREASES) | Current − Previous (positive) | Fall column | Ground dropped; staff base is lower |
| Previous reading > Current reading (DECREASES) | Previous − Current (positive) | Rise column | Ground rose; staff base is higher |
Worked Example
Station BS IS FS Rise Fall RL
A 1.50 – – 100.00
B 2.30 – 0.80 99.20 ← reading increased (1.50→2.30); FALL = 0.80
C 1.80 0.50 – 99.70 ← reading decreased (2.30→1.80); RISE = 0.50
A 1.50 – – 100.00
B 2.30 – 0.80 99.20 ← reading increased (1.50→2.30); FALL = 0.80
C 1.80 0.50 – 99.70 ← reading decreased (2.30→1.80); RISE = 0.50
Intuitive Explanation
| Staff Reading | Position of Ground | Ground Movement |
|---|---|---|
| Increases (e.g. 1.5 → 2.5) | Ground is lower; line of sight intercepts staff higher up | Ground FELL |
| Decreases (e.g. 2.5 → 1.5) | Ground is higher; line of sight intercepts staff lower down | Ground ROSE |
- Staff reading increases between two points → ground fell → record difference in Fall column.
- Staff reading decreases → ground rose → record in Rise column.
- RL(new) = RL(previous) − Fall OR = RL(previous) + Rise.