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174/3336–9FE Reference Handbook 10.4 · Surveying · Differential Leveling
1. Height of Instrument2. Differential Leveling Closure3. Azimuth and Bearing4. Latitude and Departure5. Traverse Closure and Precision6. Slope Distance to Horizontal7. Tape Temperature Correction8. Area by Coordinates (Shoelace)9. Stadia Distance10. Photo Scale11. Curvature and Refraction12. Trigonometric Elevation Difference13. Double-Meridian-Distance Area14. Circular Curve: Tangent and Length15. Missing Course of a Traverse16. Compass (Bowditch) Rule17. Vertical Curve Elevation18. Prismoidal Earthwork Volume19. Circular Curve External and Middle Ordinate20. Magnetic Declination21. Three-Wire Leveling22. Percent Grade and Slope Distance23. Latitudes, Departures, and Closure

Handbook formula

Height of Instrument

Backsight (BS) is the rod reading on a point of known elevation; it establishes the height of instrument HI. Foresight (FS) is the rod reading on a new point. Elevation = HI − FS. A turning point (TP) is both an FS and the next BS.

Height of instrument
Backsight rod reading
Foresight rod reading
Elevation of the point

Step-by-step solved example

BM elevation = 412.350 ft. BS = 4.862 ft. FS on TP1 = 6.104 ft. Find HI and Elev_TP1.

BSFSHI
HI = Elev + BS; new Elev = HI − FS. Instrument in the middle.

  1. 1. HI

    HI = 412.350 + 4.862 = 417.212 ft.

  2. 2. TP1

    Elev = 417.212 − 6.104 = 411.108 ft.

Answer: HI = 417.212 ft, Elev_TP1 = 411.108 ft

10 practice questions

0/10 correct

1.HI = Elev +

2.BM = 100.000 m, BS = 1.452 m, FS = 2.110 m. New elevation is

3.A plus sight (backsight) is taken on a

4.If FS > BS on a single setup, the foresight point is

5.An intermediate foresight (IFS) uses the same HI to get

6.HI = 87.440 m and the rod reads 1.255 m. Elevation is

7.Turning point is occupied with

8.If the rod is not plumb, the reading is

9.A dumpy or automatic level measures

10.BM = 250.00 ft, BS = 5.21, FS = 5.21. Elevation of FS point is