 # How to Measure with a Surveying Laser Level Leveling involves finding the difference in height between two points – for example, the surface of a river and the top of a levee, or ground level and a hilltop. To eliminate systematic errors related to atmospheric conditions or to residual line-of-sight error, your instrument should be about equidistant from the two points. You create a basic reference point for accurate horizontal and vertical measurements by adjusting the level so that it's true to the actual horizontal and vertical planes.

Height Difference Between 2 Points

To calculate height difference, find the difference between staff readings for the backsight (A) minus the foresight (B).

Measuring Distances Optically with the Level

The vertical cross-hair of the reticle (the viewfinder's internal target) is crossed by two short stadia lines parallel to the horizontal cross-hair. Look through the eyepiece and note the distance between the upper stadia line and the horizontal cross-hair. Now, read the distance between the horizontal cross-hair and the lower stadia line. Subtract the lower distance from the upper and multiply by 100. That's your distance reading.

Line Leveling

If points A and B are far apart, you can find the height difference between them by line leveling. Use target distances generally between 30-50 meters. Pace out the distances between the instrument and the two staffs; they need to be about the same.

Finding the Height Difference

1. Set up the instrument at S1.
2. Set up the staff precisely vertically at point B; read off and record the height (backsight R).
3. Set up the staff at the turning point 1 (ground plate or prominent ground point); read off and record the height (foresight V).
4. Set up the instrument at S2 (the staff remains at the turning point 1).
5. Carefully rotate the staff at the turning point 1 so that it faces the instrument.
6. Read off the backsight and repeat the process (S3, S4, etc.) as needed until you reach the end.

The height difference between A and B is equal to the sum of the backsight and the foresight.

Staking Out Point Heights

Say you have an excavation where point B needs to be set out one meter below street level. Measure it this way:

1. Set up the level so that the sighting distances to points A and B are about the same.
2. Set up the staff at point A and read off the backsight R.
3. Now set up the staff at B and read off the foresight V. To find the difference h from the required height at B, use the formula h = V − R − ∆H.
4. Drive in a post at point B and mark the required height.

Another way to accomplish this task is to calculate the required staff reading in advance. Use the formula V = R − ∆H. Then, move the leveling staff up or down until you can read off that required value in the level.

Longitudinal and Transverse Profiles

If you need to plan and stake out a communications route (e.g., a road), calculate fill, and/or accommodate the route to the topography as much as possible, use longitudinal and transverse profiles.

Longitudinal Profiling

1. Stake out and station the longitudinal axis by establishing and marking points at regular intervals.
2. Use the line level to determine the heights of the station points. This is the longitudinal profile.

Transverse Profiling

1. At right angles to the roadline, record at each of the station points and prominent topographic features.
2. Find the ground heights for each of the points in the transverse profile, using the known instrument height:

◦     Position the staff at a known station point. The instrument height equals the sum of the staff reading and the station point height.

◦     At each point on the transverse profile, subtract the staff reading from the instrument height. This gives you the height of each point.

◦     You can measure the distances from the station point to each point in the transverse profile, either with surveyor's tape or optically with the level.

A longitudinal profile drawing will show the heights of the station points at a much larger scale (e.g., 10x) than those in the longitudinal direction, which is related to a round reference height.