When you set up your laser tracker you'll see two values labeled L and T on a screen. This article explains what they mean, where to find them, and how they affect whether the system can use 2D stationing and elevation measurement.
Quick answer: L is longitudinal tilt and T is transverse tilt — the two directions the tracker can lean away from level. The lower the numbers, the more level the tracker. The tracker's sensor measures tilt above the rotation axis, meaning that values will change when the tracker head rotates.
If you are measuring floor elevation, both L and T values need to be below 20 at any tracker head rotation. The FieldPrinter system checks this while stationing with elevation measurement enabled.
When both L and T are below 90, the tracker is level enough for 2D stationing (on Radio 2 setups only — see below). This will give the best tracker stationing possible and can compensate for minor elevation issues in control points.
Where you see the L and T values
Which screen shows the values depends on your tracker:
| Tracker | Radio | Where the L / T values appear |
|---|---|---|
| AT930 | Radio 1 | On the tracker controller screen (the leveling page) |
| AT930-NRT | Radio 2 | On the Radio 2 screen |
| AT500 | Radio 2 | On the Radio 2 screen |
| Any Tracker | Radio 3 | On the Radio 3 screen |
What L (longitudinal) and T (transverse) mean
Both values measure how far the tracker is leaning away from perfectly level, in two different directions:
- L — longitudinal tilt is the forward/backward lean (pitch) in the direction the tracker is pointing.
- T — transverse tilt is the side-to-side lean (roll) perpendicular to the direction the tracker is pointing.
A perfectly level tracker reads 0 for both. The bigger the number, the more the tracker is tilted in that direction.
The numbers are not degrees or radians
The L and T values are display units corresponding to 1/20000th of a radian or 0.00286°. 0 means the tracker is perfectly level, and lower is always more level. The scale is proportional, so you can convert any reading to degrees of tilt: a value of 90 equals 0.258°, which works out to roughly 0.00286° per unit.
| L or T value | Approx. tilt |
|---|---|
| 0 | 0° (level) |
| 20 | ≈ 0.057° (elevation measurement cutoff) |
| 90 | ≈ 0.258° (2D stationing cutoff) |
Why the L and T values matter: Floor Elevation
To measure Floor Elevation with the FieldPrinter, the tracker must be stationed very close to perfectly level (less than 20 units). Then floor elevation can be tracked on the Dusty App and Dusty Portal and used for various applications.
When stationing with floor elevation enabled, the tracker will take about 45 seconds to automatically rotate through 4 positions to confirm it is level enough to proceed.
Why the L and T values matter: 2D Stationing
Dusty picks the best stationing method for your setup automatically. When the tracker is very close to level, the system can use 2D stationing, which compensates for small vertical (Z) differences between control point files and field conditions.
The tracker is level enough for 2D stationing when both L and T are below 90 — that is, less than 0.258° of tilt. If either value is 90 or higher, the tracker isn't level enough and the system falls back to 3D stationing.
Important — 2D stationing requires an AT500 or AT930-NRT tracker and Radio 2 with a software version of 2.9 or later. Contact your Dusty Customer Success representative if you need different equipment for an upcoming project.
How to lower the L and T values
- Adjust the tripod legs to bring the tracker toward level. Start with the physical bubble level and watch the L and T values as you go.
- Make sure the tripod is on stable, firm ground and fully tightened.
- Re-check the values after any adjustment. Both should read below 90 for 2D stationing and below 20 for elevation measurement, including after rotating the tracker head.