Calculate reduced levels (RL) and instrument height (HI) from backsight, intermediate, and foresight readings with automatic arithmetic leveling checks.
Formula and method
The Height of Instrument (HI) method establishes the elevation of the line of sight by referencing a known benchmark elevation (BM) and backsight (BS), allowing subsequent calculations of station Reduced Levels (RL) using Foresights or Intermediate Sights.
HI = BM + BS \quad , \quad RL_{station} = HI - SIGHT
Record the elevation of the known Benchmark (BM).
Add the Backsight (BS) rod reading to obtain the Height of Instrument: HI = BM + BS.
Obtain the Reduced Level (RL) of other locations by subtracting the station rod reading: RL = HI - FS (for Foresight) or RL = HI - IS (for Intermediate Sight).
Determine the difference in elevation between stations or overall vertical elevation delta.
Frequently asked questions
What is the Height of Instrument method?
The HI method establishes the elevation of the instrument line of sight by adding the backsight reading to the known benchmark elevation. Reduced levels of unknown points are then computed by subtracting rod readings from the HI.
Can I record multiple survey points?
Yes. The calculator supports multiple foresight and intermediate sight readings from a single instrument setup. Each point receives its own reduced level calculation.
How is the elevation difference calculated?
The elevation difference between any two points is computed as the difference in their reduced levels. The calculator also tracks the total vertical elevation change across the traverse.
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Calculations are preliminary estimates for planning and education.
Verify results against project documents and applicable codes with a licensed Professional Engineer.
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