Which statement correctly describes the foresight (FS) reading?

• A. Reading on a rod held on a point whose elevation is to be determined.
• B. An intermediate point between two bench marks.
• C. Elevation of the line of sight of an instrument.
• D. Reading taken on a rod held on a point of known or assumed elevation.

Answer: (A)

In leveling, the foresight reading is the staff reading taken on a rod held at a point where you want to determine the elevation. This reading is used together with the height of the instrument (HI), which you establish from a backsight on a known elevation, to compute the unknown elevation of the foresight point. The idea is that you’re forecasting or estimating the elevation of a point ahead by subtracting the FS reading from the HI to get that point’s elevation. The other descriptions don’t fit as well: a point between benchmarks isn’t specifically tied to an unknown elevation, the change in the line of sight height isn’t a rod reading, and a reading taken on a rod at a point of known or assumed elevation describes a backsight used to set the instrument height, not the future point’s elevation.