Height of Collimation Worksheet
Reduces levelling field books by the height-of-collimation method, computing reduced levels from backsights and foresights.
Field book
| BS | IS | FS | Remark | |
|---|---|---|---|---|
First row needs a backsight (BS). A change point has both a foresight (FS) and the new backsight (BS). Runs in your browser — nothing is uploaded.
Reduced levels — Height of Collimation
| Remark | BS | IS | FS | HPC | RL |
|---|---|---|---|---|---|
| BM (start) | 2.000 | 102.000 | 100.000 | ||
| Station 1 | 1.500 | 102.000 | 100.500 | ||
| CP | 1.800 | 0.500 | 103.300 | 101.500 | |
| BM (end) | 1.000 | 103.300 | 102.300 |
✓ Arithmetic check balances — the columns agree.
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the starting reduced level (RL) for the first benchmark.
- Enter the BS, IS and FS readings in order; the first row's backsight sets the first height of collimation.
- Read the reduced levels, the height of collimation for each setup, and the balance check.
How it works
The Height of Collimation (or height-of-instrument) method works from the line of sight: HPC = RL + BS. Every reading's reduced level is then RL = HPC − reading, and a change point sets a new HPC from its backsight.
The check is ΣBS − ΣFS = last RL − first RL. It's quicker than Rise and Fall for lots of intermediate sights, but it doesn't independently check each intermediate reading.
Worked example
BS 2.000 at RL 100.000. HPC = 102.000. After a change point and a final FS of 1.000 the run finishes at RL 102.300, with ΣBS−ΣFS = last−first RL = 2.300.
Tips
- The HPC check only proves the backsights and foresights — intermediate sights aren't independently checked, so read them carefully.
Frequently asked questions
Rise & Fall or Height of Collimation?
Both give the same reduced levels. Height of Collimation is faster when there are many intermediate sights (e.g. cross-sections); Rise and Fall checks every reading, so it's preferred where accuracy matters most.
Is this official course material?
No. It is free study support mapped to surveying course levels — not official North Metropolitan TAFE content or advice. Always follow your lecturer and the official assessment brief, and check your own working.
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Cite this tool
Zerdly. (2026). Height of Collimation Worksheet. Retrieved from https://www.zerdly.com/tools/height-of-collimation-worksheet/
Tip: Enter any known values to calculate the remaining results.
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