# GNSS tilt sensors

This topic applies to Trimble receivers with built-in tilt sensors, including inertial measurement unit (IMU) or a magnetometer tilt sensor.

Trimble receivers with built-in tilt sensors contain accelerometers that are used to calculate the degree of tilt of the receiver. These tilt sensors enable you to make sure the pole is vertical and stable, so that the receiver is level, or is within tilt tolerance.

Trimble receivers with built-in sensors also provide tilt compensation, which allows you to measure points when the pole is tilted and the receiver is not level. The type of tilt compensation available depends on the receiver. Options are:

- IMU tilt compensation: Trimble R780 and R12i receivers
- Magnetometer tilt compensation: Trimble R10 and R12 receivers

Well-calibrated tilt sensors are essential for accurate results. Trimble Access provides a number of calibration routines for your receiver. To view the Sensor calibration screen, tap and select Instrument / Tilt sensor options and then tap the Calib. softkey.

GNSS eBubble

The GNSS eBubble is an electronic representation of the degree of tilt of the receiver. Use the GNSS eBubble to ensure the pole is vertical, still and stable when measuring a point.

The GNSS eBubble appears automatically when you are using a:

- Trimble R10 or R12 receiver and Tilt functions are enabled in the survey style.
- Trimble receiver with IMU tilt compensation where eBubble functions are enabled in the survey style and the receiver is operating in GNSS-only mode.

For more information, see GNSS eBubble tilt sensor.

IMU tilt compensation

IMU sensors continuously determine the orientation and degree of tilt of the receiver. When combined with GNSS the receiver can continuously determine its position and correct for any amount of tilt.

IMU tilt compensation does not require a particular measurement method. When IMU tilt compensation is enabled and the IMU is aligned, IMU tilt compensation is "always on" while roving, navigating, or when measuring points using any measurement method except observed control point.

For more information, see IMU tilt compensation.

Magnetometer tilt compensation

Trimble R10 and R12 receivers have a built-in magnetometer that allows you to measure points with a tilted pole using the Compensated point method. A compensated point uses the magnetometer to calculate the direction of tilt.

For more information, see Magnetometer tilt compensation.