Choosing the right method for booking your levelling data isn’t just a matter of preference—it can affect your efficiency, accuracy, and ability to spot errors before they become costly. In land surveying, the two most common methods for recording and reducing level readings are the Rise and Fall method and the Height of Collimation (HC) method. While both are tried and trusted, each has its strengths and is better suited to particular scenarios. In this guide, we’ll break down how each works, when to use them, and how to decide which is right for your next project.
On this website, we’ve already covered detailed, step-by-step guides with worked examples for both the Rise and Fall and Height of Collimation methods. In this post, we’ll compare the two approaches, explain how each one works, and help you decide which method is right for your next project.
What Are the Rise and Fall and Height of Collimation Methods?
Comparison Table
| Feature | Rise and Fall | Height of Collimation |
| Error Checking | Strong, continuous | Limited (end of run only) |
| Speed | Moderate | Fast |
| Complex Runs | Excellent | Good, but less detail |
| Ease for Beginners | Moderate | Very easy |
| Best For | Complex/critical work | Long, simple runs |
Rise and Fall Method:
This method involves calculating the difference between consecutive staff readings to determine whether the ground is rising or falling between points. It’s a method that gives you detailed insight into every change along your levelling run and is excellent for error checking.
Height of Collimation Method:
With this method, you calculate the height of your instrument’s line of sight (collimation) at each setup. Each staff reading is then subtracted from this height to give the Reduced Level (RL) for every point. It’s a faster approach for straightforward jobs and long runs with few intermediate points.
Want the step-by-step details? See my guides for the Rise and Fall method and the Height of Collimation method.
How Each Method Works.
Rise and Fall Method.
The Rise and Fall method is a systematic approach to levelling that focuses on the differences between consecutive staff readings to determine whether you’re moving up (a rise) or down (a fall) as you proceed through your survey route. The main goal is to meticulously track every change in elevation between points, which provides not only a running check on your calculations but also makes it easier to spot errors as you go.
The process begins by taking a backsight reading on your starting benchmark or known point. As you move along your traverse, you take intermediate sights (if required) and then a foresight at the next turning point. For every new reading after the initial backsight, you subtract the previous reading from the current reading. If the result is positive, it represents a rise (the next point is higher); if it’s negative, it indicates a fall (the next point is lower).
By recording these rises and falls for each step, you can then adjust the Reduced Level (RL) of each subsequent point relative to the starting benchmark. This method is very effective at revealing arithmetic mistakes, as the sum of all rises minus the sum of all falls should match the difference between the starting and ending RLs. This continuous check is invaluable, especially on complex sites where ground undulations or frequent instrument moves could lead to cumulative errors.
Many surveyors favour the Rise and Fall method when working on projects that demand high accuracy or where error detection is critical. Because each change is individually recorded and checked, the method provides a layer of built-in quality assurance. However, this method does require more calculations and careful record-keeping, especially for long runs or jobs with many turning points.
The Rise and Fall method is particularly well-suited for use in double run levelling. Because it tracks every individual rise and fall between points, it makes comparing the forward and reverse runs straightforward and transparent. By carefully booking and cross-checking results in both directions, surveyors can spot any inconsistencies early, reduce the impact of systematic errors, and ensure that final reduced levels are as accurate as possible.
Rise and Fall Method Summary.
How it Works:
- For each pair of consecutive readings, subtract the previous reading from the current one.
- If the result is positive, it’s a rise; if negative, it’s a fall.
- Add/subtract these rises and falls to your starting RL to find the RL for each point.
Example Calculation:
- Back Sight (BS): 1.250 m, Intermediate Sight (IS): 1.700 m, Fore Sight (FS): 2.000 m
- Rise/Fall between points: 1.250 to 1.700 = Fall of 0.450 m
- Continue through the run, calculating and recording rises and falls.
Pros:
- Excellent for error checking (arithmetic checks throughout).
- Makes it easy to spot mistakes in recording or calculation.
- Useful on uneven or changing ground.
Cons:
- Slightly slower to record, as every change must be logged and checked.
- More calculations required, especially on long runs.
The above spreadsheet is available from Lichfield Survey Supplies. Rise and Fall Spreadsheet.
Height of Collimation Method
The Height of Collimation (HC) method offers a different approach, one that often prioritizes speed and simplicity. Instead of focusing on the relative change between each pair of points, this method centres on the height of the instrument’s line of sight—known as the collimation or instrument height—at each setup.
You begin with a backsight reading on your starting benchmark. By adding this backsight reading to the RL of the starting point, you establish the Height of Collimation for your current instrument position. This value represents the elevation of your instrument’s line of sight above a chosen datum.
Once the Height of Collimation is established, you subtract each subsequent staff reading (intermediate and foresight) from the collimation height to calculate the RL for every other point observed from that instrument setup. When it’s time to move the instrument to a new location, you repeat the process: take a new backsight on a turning point, calculate the new HC, and continue subtracting staff readings.
The HC method is particularly efficient for surveys with long runs and few changes in ground elevation. It reduces the number of calculations needed for each setup, as all points from one position are referenced back to a single instrument height. This makes it easy to record and follow, especially for new or less experienced staff.
However, because the HC method doesn’t involve calculating rises and falls at every step, it’s less robust for spotting recording or calculation errors until the very end of the survey. For straightforward, repetitive jobs, this is often an acceptable trade-off, but for complex sites, you may want more frequent error checking.
Height of Collimation Method Summary
How it Works:
- After each instrument setup, calculate the Height of Collimation (HC) by adding the BS to the RL of the known point.
- Subtract each subsequent IS and FS from the HC to get the RL of new points.
- Move instrument, repeat for the next setup.
Example Calculation:
- Known RL: 100.000 m, BS: 1.200 m → HC = 101.200 m
- IS: 2.150 m, RL = HC – IS = 101.200 – 2.150 = 99.050 m
- FS: 2.500 m, RL = 101.200 – 2.500 = 98.700 m
Pros:
- Fast and simple for straightforward jobs.
- Fewer calculations if there are many intermediate sights from one setup.
- Easy to follow for new staff.
Cons:
- Not as strong for error checking—mistakes may go unnoticed until the end.
- Less detail about ground rises and falls between points.
When to Use Each Method
- Use the Rise and Fall Method when:
- You want robust error checking at every stage.
- The ground profile is complex or changes frequently.
- Accuracy is critical, or multiple team members are working on the same run.
- Use the Height of Collimation Method when:
- You’re working on long, straight runs with fewer changes in ground profile.
- Speed is important, and you’re confident in your data collection.
- The project is straightforward (e.g., road or pipeline levelling).
A spreadsheet for working out the Height of Collimation is available from Lichfield Survey Supplies Ltd. Height of Collimation Spreadsheet.
Comparison Table
| Feature | Rise and Fall | Height of Collimation |
| Error Checking | Strong, continuous | Limited (end of run only) |
| Speed | Moderate | Fast |
| Complex Runs | Excellent | Good, but less detail |
| Ease for Beginners | Moderate | Very easy |
| Best For | Complex/critical work | Long, simple runs |
Frequently Asked Questions
Q: Which method is easier for beginners?
A: The Height of Collimation method is usually easier to learn and apply, but the Rise and Fall method teaches good habits for error checking.
Q: Can I switch between methods during a survey?
A: No. It’s best to stick to one method per booking sheet or project, but understanding both allows flexibility if required. Often when recording levels out on site you will only take one book with you, either the Collimation book or the rise and fall book.
Q: Which is better for long levelling runs?
A: The Height of Collimation method is faster for long, uncomplicated runs, while the Rise and Fall method provides more opportunities to check for mistakes.
Double Run Levelling: Adding Accuracy and Error Control
For projects that demand high precision—such as establishing benchmarks, setting control points, or working on critical infrastructure—surveyors often employ double run levelling. In this method, the levelling run is carried out twice: once in the forward direction (from start to finish) and then again in the reverse direction (from finish back to start), using the same stations and turning points both ways.
The primary goal of double run levelling is to identify and reduce systematic errors that may creep into a survey due to instrument maladjustment, staff inconsistencies, or simple mistakes in reading or recording. By comparing the results from the forward and reverse runs, any discrepancies—known as the closure error—become apparent. If the difference falls within the acceptable tolerance for the project (usually a few millimetres), the results are considered reliable and can be averaged for even greater accuracy. If not, the run should be repeated.
This technique is especially useful in important control work, long levelling runs, or when working in challenging conditions where errors could accumulate. Double run levelling adds an extra layer of quality assurance, helping to protect both your data and your reputation.
Conclusion
Both the Rise and Fall and Height of Collimation methods have their place in modern surveying. Your choice depends on the job’s complexity, your need for error checking, and personal or team preference. By understanding the strengths and limitations of each, you’ll be able to work more efficiently—and with greater confidence in your results.
Looking to master each method? Check out my step-by-step guides on Rise and Fall and Height of Collimation, and don’t hesitate to share your own experiences or questions in the comments below!
Glossary of Levelling Terminology
Backsight (BS):
A staff reading taken on a known benchmark or the starting point after setting up the instrument. Used to establish the Height of Collimation or as the initial reading in the Rise and Fall method.
Benchmark (BM):
A fixed reference point of known elevation used as a starting or finishing point for levelling.
Collimation (Height of Collimation, HC):
The height of the instrument’s line of sight above a chosen datum. Used to calculate the reduced levels of all other points from a single instrument setup.
Datum:
A reference level from which elevations are measured, often sea level or an arbitrary point on site.
Foresight (FS):
A staff reading taken on the next point to be determined or at the end of a levelling run, usually before moving the instrument.
Intermediate Sight (IS):
A staff reading taken on any point between backsight and foresight, where no instrument move occurs.
Levelling Staff:
A graduated rod (often in metres or millimetres) used with a level instrument to measure differences in elevation.
Reduced Level (RL):
The calculated elevation of a particular point relative to the chosen datum.
Rise:
An increase in ground level between two points, calculated in the Rise and Fall method.
Fall:
A decrease in ground level between two points, calculated in the Rise and Fall method.
Turning Point (TP):
A temporary point used to transfer the instrument’s line of sight from one setup to another.
Two-peg Test:
A practical test for checking the accuracy and adjustment of a levelling instrument, typically using two fixed points (pegs) at a known distance apart.
Booking:
The process of recording field measurements and calculations in a levelling field book or data sheet.
Parallax:
An optical error that occurs when the line of sight and the crosshairs of the instrument are not properly aligned, resulting in incorrect staff readings.
Compensator:
A self-levelling mechanism within an automatic level instrument that ensures the line of sight remains horizontal, even if the instrument is slightly out of level.
Datum Line:
An imaginary line representing the zero elevation or reference plane from which levels are measured.