# Aligning the IMU

To use IMU tilt compensation, you must align the IMU in the receiver. The alignment process is simple and straightforward, and mimics normal use of the receiver.

1. Attach the receiver to the survey pole.
2. Make sure you correctly enter the antenna height in the GNSS antenna form in the Trimble Access software.

3. Move the pole so that the receiver experiences acceleration and changes in position. This can range from rocking the survey pole back and forth while keeping the pole tip on the ground, to walking a short distance (generally less than 3 meters) while changing direction a few times.

   When the IMU is aligned, the receiver icon in the status bar changes from to and the status line shows IMU aligned. The precision of the current position is calculated at the pole tip.

Align the IMU when you start the survey, or during the survey when alignment is lost. You can also align the IMU without starting a survey, as long as the receiver is in a good GNSS environment so enough satellites can be tracked. When you end a survey with IMU tilt compensation enabled and the IMU aligned, IMU tilt compensation remains in use.

If you are working in a very difficult RTK environment, you may need to switch to GNSS‑only mode. To switch to GNSS‑only mode, tap the receiver icon in the status bar to view the GNSS functions screen and then tap IMU tilt compensation to toggle on/toggle off GNSS‑only mode.

IMU tilt compensation uses the antenna height to accurately compute the pole tip position. Whenever the antenna height is changed, the IMU is reset to an unaligned state. You must realign the IMU with the updated antenna height before measuring.

When measuring or staking out points using IMU tilt compensation, make very sure the entered antenna height and measurement method is correct. Alignment reliability and pole tip position reliability, especially during movement of the antenna while the pole tip is stationary, relies completely on the antenna height being correct. Residual error in horizontal position caused by antenna motion while measuring when the pole tip is stationary cannot be removed by changing the antenna height after measuring the point.

In good RTK environments the IMU reliably realigns itself automatically during natural pole movement. To realign the IMU during the survey, repeat step 3 from the Aligning the IMU section above.