How to Transfer RL by Using Auto Level – Step-by-Step Guide

In the field of civil engineering, transferring Reduced Level (RL) is one of the most essential tasks when it comes to leveling and ensuring accuracy in elevation. Whether you're working on a building foundation, roadwork, or land survey, knowing how to transfer RL using an auto level is a basic but crucial skill.

Bosak Civil Construction explore what RL means, why it's important, and how to transfer it accurately using an auto level. This guide is beginner-friendly and written in a practical tone so anyone can understand it easily.

Reduce Level

■ What is RL (Reduced Level)?

Reduced Level (RL) is the vertical distance of a point above or below a fixed reference point, usually called the benchmark. It helps in determining the height or depth of different points on a site. RLs are crucial for:
》Laying foundations
》Constructing floors at correct heights
》Ensuring slope and drainage in roads
》Comparing levels across long distances

■ What is an Auto Level?

An Auto Level (or Automatic Level) is a surveying instrument used to establish or verify points in the same horizontal plane. It helps in transferring and checking RLs by providing a level line of sight.
It consists of:

•Telescope
•Spirit level (bubble)
•Leveling screws
•Tripod stand

■ Tools Required

Before you begin, make sure you have the following tools:

1. Auto Level machine

2. Tripod

3. Levelling staff (a graduated rod)

4. Field notebook or data sheet

5. Pencil or pen

■Step-by-Step Process to Transfer RL Using Auto Level:

1. Set Up the Tripod and Auto Level
●Choose a stable and central point between the known and unknown RL points.
●Extend the tripod legs and fix them firmly into the ground.
●Mount the auto level on the tripod and tighten it securely.

2. Level the Auto Level
●Use the leveling screws to adjust the instrument.
●Center the bubble in the circular spirit level to ensure the instrument is perfectly horizontal.

3. Identify a Benchmark
A benchmark is a point with a known RL.
For example, suppose the benchmark RL is 100.000 m.

4. Take a Backsight (BS) Reading
●Place the leveling staff vertically on the benchmark.
●Look through the auto level and focus on the staff.
●Note the reading where the crosshair intersects the staff (e.g., 1.450 m). This is called the backsight (BS).

5. Calculate the Height of Instrument (HI)
HI = RL of Benchmark + BS
HI = 100.000 + 1.470 = 101.470 m

6. Take a Foresight (FS) Reading
Now move the staff to the next point where you want to find the RL.
Take the reading through the auto level (e.g., 1.250 m).
This is the foresight (FS).

7. Calculate the RL of New Point
RL = HI – FS
RL = 101.450 – 1.250 = 100.200 m
That’s it! You have successfully transferred the RL from the benchmark to a new point using an auto level.

■ Example Summary in Table Form

Observation Reading (m) Calculation Result (m)

Backsight (BS) 1.450 100.000 + 1.450 (HI) 101.450 (HI)

Foresight (FS) 1.250 101.450 – 1.250 (RL) 100.200 (New RL)

■ Tips for Accurate RL Transfer:

Always ensure the auto level is properly leveled before taking readings.

●Use firm ground for the tripod to avoid errors.
●Take multiple readings and average them if needed.
●Make sure the staff is vertical—use a bubble if needed.
●Avoid doing this task in windy or unstable environments.

Conclusion:

Transferring RL using an auto level is a standard process in any construction or surveying project. With practice, you’ll be able to do it quickly and accurately. Always remember that even small errors can lead to major issues in construction, so precision matters. Whether you're a student, site supervisor, or just curious about leveling, this method will help you understand and apply the concept of RL transfer confidently.