How a level line works
A level gives you a horizontal line of sight. Everything else is arithmetic. Sight back to a point of known elevation and add the rod reading: that is the height of instrument, HI = Elev + BS. Sight forward to the new point and subtract: Elev = HI − FS. Every setup repeats those two steps, and a turning point is just a foresight that becomes the next backsight.
The page check proves you reduced the notes correctly: ΣBS − ΣFS must equal the ending elevation minus the starting elevation. It catches arithmetic, not field blunders. ΣBS equals ΣFS only when the line ends at the elevation it started.
The one procedure the exam always asks about
Balance the backsight and foresight distances. When the two sights are the same length, the level's collimation error and the earth's curvature and refraction affect both readings equally and cancel in BS − FS. No calibration needed. This is the single most tested fact in leveling.
Two smaller habits matter too:
- Wave the rod slowly toward and away from the instrument. Any tilt makes the reading larger, so the rod is plumb at the instant the reading is smallest. Record the minimum.
- Remove parallax by focusing the eyepiece on the crosshairs first, then the objective on the rod, until the image stops shifting against the hairs when you move your eye.
About the exam itself
One question here is about the FS format: 110 questions, 5 h 20 min of exam time inside a 6-hour appointment, closed book with the searchable NCEES Reference Handbook on screen, and one scheduled 25-minute break.