In surveying, “HI” means Height of Instrument. The term is used when:
- Describing the elevation or height a total station is above a survey mark that it is set up on, or
- The elevation of an automatic/dumpy level based on a known benchmark elevation.
How to Calculate Height of Instrument (HI)
When undertaking a level survey run, to calculate the height of an instrument, the formula is:
Benchmark Elevation + Backsight Observation = Height of Instrument
What Errors Can Cause Inaccuracies in Height of Instrument Reading
There are several systematic and human errors that can cause inaccuracies in the height of instrument reading. These include:
- Not having an equal foresight and backsight distance.
- The level bubble on the dumpy level or staff is out of adjustment.
- Unstable change point marks.
- Not having the leveling rods correctly extended on the leveling staff.
